PurposeOrganisations increasingly rely on professional interim managers (PIMs), i.e. independent contractors who perform managerial work. These managers, who are usually very experienced and skilled, could help organisations drastically improve their performance. However, research has found that they often fail to do so, indicating that PIMs face unique on-the-job challenges that challenge their capability to be effective managers. In the study reported in this paper, I explored PIMs’ on-the-job challenges and how they overcome them. To better understand the various on-the-job challenges, I developed the concept of the liability of outsiderness.Design/methodology/approachI applied an exploratory approach and conducted 32 interviews with 21 PIMs.FindingsI uncovered three on-the-job challenges common and unique to PIMs – communicating the contract status and contract period, being quick off the mark and attaining power – and the ways they overcome these challenges.Practical implicationsThis paper reports findings and theory that provide several valuable guidelines for practitioners involved with interim management.Originality/valueInterim management has received little scholarly attention despite its increasing relevance. Empirical research, particularly on PIMs in executive positions, is lacking. This leaves us with little evidence to base our theories and guidelines for interim management. The study reported in this paper adds novel insights to an under-researched but important field of management. The study also introduces the liability of outsiderness concept, which holds much promise for future studies of interim management.