[Don Plumley]

Depending upon your role, it might indicate your propensity for "grass is greener" syndrome or it might not be a big deal at all.

You were at the first company for just over one year. At the current company for 18 months. So you are trading down in seniority/tenure which is a consideration if you are concerned about layoffs.

You should change jobs because a) gain responsibility/skills that are useful to you; b) think you will enjoy the work and working environment more; c) will make a lot more money. Changing because you sense more stability might be short-sighted if you don't like the work.

As to your specific question - if there is a good reason, a move back after 18 months wouldn't be a negative in my book, so long as less than two months (I made a big mistake) or more than two years (time to move on) elapse when you are next looking.