Since its third iteration in 2008, the international Concussion in Sport Group (CISG) has delineated several ‘modifying factors’ that have the potential to influence the management of sport-related concussions (SRC). One of these factors is co- and pre-morbidities, which includes migraines, mental health disorders, attention-deficit hyperactive disorder (ADHD), learning disability, and sleep disorders. Mental health disorders, and in particular, depression, have received some attention in the management of SRC and in this review we summarize the empirical evidence for its inclusion as a modifying factor. This review is divided into three main bodies of findings: (1) the incidence and prevalence of depression and depressive symptoms in non-concussed and concussed athletes, with comparison made to the general population; (2) managing the post-concussion athlete and accounting for premorbid depressive symptoms; and (3) depression as a long-term effect of repetitive head trauma. Overall, it has been reported that certain subpopulations of athletes have similar or even higher rates of depressive symptoms when compared to the general population. The challenge of accounting for these baseline-depressive symptoms while managing the post-concussive athlete is stressed. And lastly, the prevalence of depression and its relationship to concussion in later-life is discussed.