Sertoli cell tumours (SCT) are rare and poorly explored neoplasias, and the genetic features of these uncommon tumours are largely unknown. Data about chromosomal aberrations in human SCT of the testis are very rare. We present in this paper the first molecular-cytogenetic study of SCT of the testis. DNA was isolated from paraffin-embedded tumour material from 11 patients with unilateral SCT. We used comparative genomic hybridisation to investigate changes in DNA copy number. The detected DNA imbalances showed variation from case to case, indicating a high genetic heterogeneity. Chromosomal aberrations were detected in 9 of the 11 tumours evaluated, with 13 losses versus 14 gains. The most frequent aberrations detected were gain of chromosome X (5 of 11 cases) followed by losses of entire or part of chromosomes 2 and 19 in three cases. This study suggests a high variability in histomorphological and genetic patterns. Only gain of the entire chromosome X seems to be a frequent aberration in these tumours. Further studies of these tumour types are necessary to clarify the significance of chromosomal alterations in carcinogenesis of SCT.