We report on an adenoid cystic-carcinoma (ACC) with a clonal deletion of 17p as the only karyotypic abnormality. Using different chromosome 17-derived probes we showed by FISH that the deletion encompassed the p53 tumour suppressor gene. Immunohistochemical analysis revealed overexpression of p53 protein in a subpopulation of cells, suggesting a mutation in the remaining p53 allele in these cells. Our findings provide novel information about possible progressional pathways in ACC, and demonstrate the value of combining conventional cytogenetic analysis with-molecular cytogenetic and immunohistochemical methods. This approach is particularly useful in cases with minor cytogenetic abnormalities at the border of visibility.