In sport, optimizing weight and body composition is important for performance although an excessive drive for thinness can lead to diminished performance and health problems. This is especially important in the youngest athletes. This study examines 60 national competition-level Spanish artistic swimmers aged 9-17 years. Participants were divided into 3 categories: 12 years and under, 13-15 and 16-17 years. The data analysed were anthropometric measures, menarche age, genotype related to performance (gene ACTN3) and athletic performance. Relationships between athletic performance and anthropometric or genetic data were compared among the three age groups. Swimmers showed a tendency to carry the heterozygous genotype RX of the ACTN3 gene in the older age group. In this study, this sport could have an impact on body mass index, triceps skinfold, weight, menarche age, and selection of one genotype, but the performance in competition of the artistic swimmers had little linking to anthropometric measures.