Beunen et al. (1978) found that the early maturers in their sample of non-athletic girls performed better on simple motor tasks than the late maturers early in adolescence, but that the late maturers performed better than the early maturers late in adolescence. PURPOSE: To determine if the same relationship between maturational timing and performance exists when high-level athletes execute complex motor tasks. METHODS: NCAA women swimmers (N = 254) completed an online questionnaire in which they provided age, height, weight, swimming history, and age at menarche (AaM). We divided the sample into early-, average-, and late-maturing groups using AaM. We utilized the USA Swimming (USAS) performance database to identify individual performances for each swimmer at three adolescent phases: (1) early adolescence (12 years old), (2) middle adolescence (15 years old), and (3) late adolescence (18 years old). Each performance in the USAS database equates to a standardized score called a Power Point Score (PPS). We selected the highest PPS for each swimmer at the three adolescent phases. We analyzed the data using a Two-way Mixed Design ANOVA. RESULTS: Mean AaM values for the early-, average-, and late-maturing groups were 12.0 years (95% CI, 11.8 to 12.2), 13.4 years (95% CI, 13.3 to 13.5), and 15.4 years (95% CI, 15.2 to 15.6). We identified performances for 173 of the 254 respondents (68.1%) in the USAS database at all three adolescent phases. We detected a significant two-way interaction (F4,334 = 5.8, P < 0.001), which indicated that the effect of maturational timing on swim performance differed by adolescent phase. Mean PPS for the early, average, and late maturers during early adolescence was 496.4, 494.8, and 480.0, whereas mean PPS during middle adolescence was 664.4, 683.1, and 721.3. Thus, the late maturers improved more (62.6%) from early to middle adolescence than the average (47.0%) and early (45.2%) maturers. In contrast, swim performance improved to a similar extent for the three groups from middle to late adolescence. CONCLUSION: Our results extend Beunen et al.’s findings by showing that early-maturing swimmers have a performance advantage over late-maturing swimmers during early adolescence. But by middle adolescence, the late maturers have a performance advantage that is maintained into late adolescence.