Testicular cancer (TC) is the most common solid tumour in white males aged 20-34 years, and its incidence has doubled over the past 40 years. Some risk factors for TC have been proposed, such as cryptorchidism, infertility and testicular dysgenesis. However, the causes of TC remain still largely unknown. Recently a genetic basis for TC has been proposed, but specific genetic alterations have not been identified. The risk of TC is markedly increased in subjects with androgen insensitivity and some authors have suggested that mutations in the androgen receptor (AR) gene or disorders of CAG and GGC repeats could be related to TC. However, definitive data have not been produced. In this study, we analysed the AR gene for mutations and CAG and GGC triplets in exon 1 in 123 patients affected by TC. In three patients (2.3%) we found a mutation in the AR gene, two of which represent a novel mutation. Evaluation of CAG and GGC repeat numbers showed no difference with respect to controls when these variables were analysed separately. However, when joint distributions of CAG and GGC were considered, we found that the combination CAG=20/GGC=17 was significantly more frequent in TC patients (8.1%) with respect to controls (1.7%, P<0.05). Furthermore, we observed that in TC subjects, differently from controls, the joint analysis of CAG and GGC showed a statistically significant dependence among these variable repeats. In conclusion, our data show for the first time a high prevalence of AR gene mutations in patients affected by TC and suggest that some CAG/GGC combinations might be more frequently associated with an increased risk of TC.