The exon-1 of the androgen receptor (AR) gene contains two repeat length polymorphisms which modify either the amount of AR protein inside the cell (GGNn, polyglycine) or its transcriptional activity (CAGn, polyglutamine). Shorter CAG and/or GGN repeats provide stronger androgen signalling, and vice versa. To test the hypothesis that CAG and GGN repeat AR polymorphism affects muscle mass and various variables of muscular strength phenotype traits, the length of CAG and GGN repeats was determined by PCR and fragment analysis, and confirmed by DNA sequencing of selected samples, in 282 men (28.6 ± 7.6 years). Individuals were grouped as CAG short (CAGS) if harbouring repeat lengths of ≤21 and CAG long (CAGL) if CAG >21. GGN was considered short (GGNS) or long (GGNL) if GGN ≤23 or > 23, respectively. No significant differences in lean body mass or fitness were observed between the CAGS and CAGL groups, or between GGNS and GGNL groups, but a trend for a correlation was found for the GGN repeat and lean mass of the extremities (r=-0.11, P=0.06). In summary, the length of CAG and GGN repeat of the AR gene do not appear to influence lean mass or fitness in young men.