Serum vitamin D concentrations (25[OH]D) are associated with physical performance in the general population, but few studies have been published in athletes. 80 competitive adolescent swimmers from both sexes were tested for serum 25(OH)D concentrations, grip strength, balance and swimming performance at several speeds. Spearman’s correlations were used to examine the associations between 25(OH)D concentrations and age-adjusted measures of performance. Performance parameters were also compared between vitamin D sufficient (n = 27), insufficient (25[OH]D ranging 20−29.9 ng/ml, n = 42), and deficient (25[OH]D < 20 ng/ml, n = 11) participants. No significant associations were found between serum 25(OH)D concentrations and any of the performance measures, with no significant differences found between vitamin D sufficient, insufficient and deficient participants. In competitive adolescent swimmers, serum vitamin D concentrations were not associated with strength, balance or swimming performance. Vitamin D insufficient/deficient swimmers did not have reduced performance.