Objective: To examine the differences between participants and nonparticipants in a study of children with unilateral hearing loss that might contribute to selection bias. Study Design: Case-control study. Setting: Academic pediatric otolaryngology practice. Subjects and Methods: Comparison of clinical and sociodemographic characteristics between the 81 participants and 78 nonparticipants with unilateral hearing loss in a case-control study. Results: Compared with nonparticipants, the study participants were younger but were diagnosed at an older age. Participants were more likely to have been diagnosed through a primary care screen and have normal ear anatomy, and less likely to have an attributed etiology for their unilateral hearing loss or tried assistive hearing devices. No other significant demographic, socioeconomic, or clinical differences were identified. Conclusion: Self-selection bias may jeopardize both internal and external validity of study results and should be evaluated whenever possible. Methods to minimize self-selection bias should be considered and implemented during the planning stages of clinical studies.