Background The role of specific phobia as a potentially important psychopathological precursor condition to more severe mental disorders is understudied. We examined the prospective‐longitudinal association of early childhood/adolescent phobia with subsequent mental disorders and the proportion of outcome disease incidence attributable to specific phobia simultaneously for a broad range of disorders. Methods N = 2210 14‐ to 24‐year‐old community subjects were followed up for 10 years. DSM‐IV‐specific phobia as exposure and a broad range of DSM‐IV mental disorders as outcomes were assessed with the DSM‐IV/M‐CIDI. Logistic regressions, adjusting for confounders, were used to estimate the associations of specific phobia with the subsequent onset of outcome disorders. Results Baseline specific phobia predicted the subsequent first onset of anxiety disorders [panic disorder: risk ratio (RR) = 4.38, 95% confidence interval (2.34, 8.21); generalized anxiety disorder: RR = 4.10 (2.19, 7.69); posttraumatic stress disorder: RR = 2.15 (1.13, 4.10); obsessive–compulsive disorder: RR = 3.79 (1.63, 8.82)], affective disorders [major depression: RR = 1.54 (1.16, 2.03); bipolar disorder: RR = 2.20 (1.10, 4.41); dysthymia: RR = 2.75 (1.48, 5.11)], pain disorder: RR = 1.52 (1.14, 2.02), and eating disorders: RR = 2.27 (1.14, 4.51). Population attributable fractions (PAFs; i.e., proportion of outcome disease incidence in the total population attributable to specific phobia) were highest for panic disorder (PAF = 22.9), generalized anxiety disorder (PAF = 32.3), and obsessive–compulsive disorders (PAF = 30.2). Conclusion This study provides strong evidence that specific phobia is an early onset disorder predicting the subsequent onset of a range of disorders. Future studies should examine the underlying mechanisms and the potential of using specific phobia as a target for prevention of subsequent psychopathology.