Working with a Ph.D. supervisor that may have to take medical leave? I'm interested in working with Professor X for my Ph.D. My first meeting with X went very well. I like him and I get the impression that we would work well together in the graduate school environment. Moreover, the research is in a field that I am extremely interested in and I think it would be a good fit for my skills. 

In speaking to the graduate students privately, I heard nothing but praise for Professor X. However, one student disclosed that he (the professor) suffers from a disability that required him to be on medical leave for over a year. The student said that this slowed the progress of research and probably delayed his Ph.D by a non-trivial amount. Otherwise, he said that he was very happy working with Professor X and would even make the same decision again.

Obviously, I think it would be inappropriate to ask Professor X about this. However, I am concerned that such a situation may arise again during the course of my Ph.D. I also don't want to discriminate against someone due to a medical condition.

So my questions are:


How problematic is it for an advisor to be unavailable for research consultation for a long period of time?
Is it unwise (or unethical) to make such a decision based on the disability of an advisor?
Would it be inappropriate to ask other graduate students about his condition and how it has affected their work?


I know that the choice of advisor is often considered the most important decision about graduate school. Professor X would be my clear first choice but I'm just having second thoughts due to potential uncertainty in the future of my Ph.D.
I'm a big fan of saying "donkey" when it's a donkey, rather than beating around the bush and calling it a grey-colored, short-legged horse.

The thing is: Everyone, including the professor, understands that any leave of absence he's going to take will affect you in a number of important ways. It's not like anyone can be mad at you for wanting to bring this up. So that's what I would do, acknowledging the awkwardness of the situation, in a personal conversation:


  Professor, I would really like to work with you, but I have one last, awkward topic I'd like to ask you. When talking to others in the department over the past couple of weeks, someone mentioned that you may take an extended leave of absence for personal reasons. It's really none of my business to ask you about this, or the reasons for this, but if I signed up with you, it would be something that clearly affects me as a graduate student. So I wanted to bring it up and see whether that was true or not.


That gives the professor an opportunity to tell you how it is. He will understand why you ask, and tell you about as much as he chooses to share. If there really are medical reasons, you're not likely going to get any better answer by going around his back and asking others in the department.

I'll also mention that over your career as a grad student, you're likely going to have a number of awkward conversations with your adviser anyway. You may have to talk about money issues (grant runs out and it's not clear if the follow-up grant will be approved), breaking up with your girlfriend and falling into a hole for a number of months, being sick for an extended time, etc. Professors have awkward conversations with students all the time, and the better ones have figured out how to have them without it being that big a deal. So talking about something you have a legitimate concern about should be par for the course.