If a candidate does not follow up after a job interview should I automatically dismiss them as a candidate?

Personally, I think that seems like a trivial reason to exclude somebody if they are qualified. Your primary objective should be to find the person who will do the best job, not has the best followup (unless the job is following up I guess. :)

I think there are other things that can influence this too?

1. How did you conclude the interview? Did you give them an expectation ("I will get back to you next week.") or did you leave it hanging assuming they would followup? I personally think you must give an expectation, and if you did, they may simply be waiting for that time to followup so as not to bother you, you're a busy guy.
2. Did they come to you through a recruiter? Do they have your contact info? Maybe they called the recruiter or receptionist and thanked them for the interview and you didn't get the message? Maybe it's in the mail? (ok, unlikely :)

I would consider a followup as a bonus if I was trying to decide between 2 equal candidates only. It usually doesn't sway my thinking on if they can do the job or not.

There is an entire body of theory about job searches. Some experts advise NOT to do a thank-you letter, for the reason that there was no exchange of value in favor of the candidate, and also because it may signal desperation for a job.

I'd treat receiving one as a very slight bonus. Some employers may view it negatively, for the reason mentioned. But other factors such as experience, skill, fit, etc would outweigh it.

The only selection criteria that you should have with respect to the candidate's behavior at this point is if they are hard to get hold of or to follow up with. If they're motivated they will return your calls easily.

Although you didn't ask about this, the second interview is generally unnecessary.

• Edit *

Actually, an important additional point occurred to me after seeing your response below. (The snark was immature, btw.)

Here's the point: are you hiring a developer, or a sales person or other client facing role? If the former, most developers are not well noted for their sales personalities, and I would consider a follow up from the candidate just about without meaning either way. If the latter, then YES, the candidate should probably be expected to take the step of sending a follow up letter or email. After all, if the person is expected to perform sales, then he should be selling himself strongly. Not following up for a sales person would be similar to a programmer flunking a tech-out.

If you want to hire quality people you need to re-evaluate biases that are destructive to that end.

If they came through a recruiter, its the recruiter's job to follow up with you not theirs, I am only speaking from experience but I would feel awkward following up directly with a company if I got the interview through a recruiter. Rather, I would talk with the recruiter to express my interest. Some recruiters are lazy and just don't get back to the candidate as soon as they should so the candidate assumes that the company isn't interested when it really was the recruiter, long story short if you're using a recruiter, ask the recruiter to follow up with the candidate to gauge their interest before dismissing them.

If you're not using a recruiter and dealing with the candidate directly, well I guess it depends. The jobs I have gotten directly with a company have been for very small companies so I was dealing directly with the owner and things were informal, so after the first interview we had already set up an "action" that would take place (either a second meeting or a small task I would do to prove my "worthiness") so this naturally led to a followup. If you end an interview by saying, "we'll be in touch", then its on you to contact them, if you don't they are going to assume you aren't interested. I would pay attention to how you're leaving things at the end of interviews if you are having a problem with this. Personally, as an interviewee I've learned to make my interest clear at the end of an interview, but only if I am actually interested. If I can tell I've gotten past their initial line of questioning to where they seem to have interest I then proceed to ask some questions such as inquiring about specifics of teams, work environment, equipment provided by them, etc and then basically make it clear that I am agreeable to everything. Then at the end, I ask how soon they are going to make a decision, etc. I feel as long as I make my interest clear, its on them to get back to me, if they haven't given me a clear "next step".

Thin-skinned?

If many of your candidates aren't following up, then that's just how interviews work, and you should consider it normal. I've sometimes sent thank-you notes for interviews, but usually not. What exactly are you looking for? Have you followed up with them to express your interest in hiring them? If not, why are you expecting them to follow up with you?

Well, it depends.

There is perhaps no need to conduct a second interview. If the short-listed candidates are truly skillful, knowledgeable and best matched with your job requirements then it’s no harm to boldly ask their willingness if they want to become your employees. But if they don’t come up with an exact answer, don’t drop them straight away, keep them queued and start hunting for other talents.

If following up on things (sales, bizdev, etc.) is critical then the follow up to the interview is critical. In other cases it is a tie-breaker or a good indication of their ability to follow up or an indication of their interest. I would never rule someone out based on this, but I would definitely use it as a bonus to otherwise similar candidates.