The present study was performed to assess the expression of isoforms 1, 2 and 3 of transforming growth factor (TGF)-beta in skin nodular dermatofibrosis lesions, kidney, bladder and pancreas from a 10-year-old female German shepherd dog (GSD) affected by renal cystadenocarcinoma and nodular dermatofibrosis (RCND) compared with normal GSDs (n = 2). Formalin-fixed, paraffin-embedded tissues obtained from the dog affected by RCND, diagnosed by renal ultrasonography and histopathological examination were analysed by immunohistochemistry using polyclonal antibodies to TGF-beta1, 2 and 3, and evaluated semiquantitatively using an immunoreactivity score. Similar expression of TGF-beta2 and TGF-beta3 was observed in all tissue specimens in both the RCND-affected animal and normal dogs. In contrast, TGF-beta1 immunoreactivity was increased in the derma of the RCND canine. Comparable TGF-beta1 serum levels were found between the diseased and normal animals. The increased local cutaneous production of TGF-beta1 in the RCND dog, compared with the normal animals, suggests that this cytokine may play an important role in the induction of nodular dermatofibrosis associated with renal cystadenocarcinoma.