While not the most common interview question, it does pop it's head up from time to time--so be prepared to answer it. Many interviewers like to ask this question because it forces the candidate to choose just one of the many skills required to be a good project manager. Technically, there is no single correct answer to this question, but you need to be cognizant of what your answer reveals to the interviewer about you, your experience and your ability.

Don't dance around the question, or be vague. Answer the question directly and provide just one answer, as requested. Your answer to this question should be what you feel is your greatest strength as a project manager (e.g. team-building skills, keeping projects on schedule, flexibility). Be prepared to explain why this skill is critical to effective project management and how it will benefit the company.