Several years ago, I pulled aside a graduate student and advised her to find a different PhD supervisor. I delicately, but clearly, pointed out that her current supervisor had a record of relating poorly to others and was seen as a source of extreme irritation by many departmental colleagues.The student was torn – for her supervisor was also charismatic, had published in prominent outlets, and had research interests that were reasonably close to her own. So she rolled the dice and maintained the relationship.Three years later, the student sat in my office completely distraught. Her supervisor would not respond to emails and phone calls and was taking forever to comment on drafts of her thesis chapters. In essence, her supervisor failed her as a mentor, her degree was in crisis, and she needed to find a new supervisor quickly.Screwing up your choice of supervisor is one of the biggest missteps you can make in graduate school. It is also easy to do. If you choose a supervisor because of a single overriding factor – such as a desire for someone who is personable, or is not intimidating, or has a big name – you risk choosing poorly.So choose carefully, and do not let any one factor sway your decision too much. Enquire about whether others recognise your potential supervisor as a solid choice. Do her students finish their degrees, and in a reasonable time? Does she publish work of high quality in prominent outlets? Does she have a record of getting her students published? Does she equitably co-author articles with her students? Is the supervisor too overwhelmed with other commitments to give you the attention you need? Has she secured research grants? What kinds of jobs did her previous students obtain? Is the supervisor immersed in her academic community?Also consider the personality of a potential supervisor. Do colleagues find her easy to work with? You should consult widely.The availability of an appropriate supervisor should definitely affect your decision about which PhD programme to attend. But if the person you have your sights set on is known as a good supervisor, there are likely to be other students seeking to work with her. If you are going to a university mainly to work with that person, make sure that she will actually work with you.