Most renal cell carcinomas are assigned to either the papillary or clear cell, non-papillary type by morphological and cytogenetic criteria. In rare cases, papillary carcinomas of the kidney have been classified as collecting duct carcinoma because of their medullary localization and the associated hyperplastic and dysplastic epithelial lesions of collecting ducts in the vicinity of the tumour. In this first report on the cytogenetics of collecting duct carcinoma, we describe unique and consistent chromosomal aberrations in three cases. Each of the three tumours showed monosomies for chromosomes 1, 6, 14, 15, and 22. This suggests that collecting duct carcinoma is the third type of kidney tumour whose definition is based on morphological as well as on cytogenetic criteria. It appears to be cytogenetically different from the cortical papillary kidney tumour which exhibits trisomy 17 and tri- or tetrasomy 7, and from the non-papillary renal cell carcinoma which characteristically presents deletion of the short arm of chromosome 3.