Cytogenetic investigation on short-term cultures of 13 nasal polyps disclosed the presence of chromosome aberrations in three cases: one (a recurrence) showed numerical changes; the other two had structural abnormalities, an inv(12)(q15q22) in one case, a der(6)t(6;12)(q22;q15) in the other. The three cases were characterized histologically by the presence of frequent atypical stromal cells, and were positive for vimentin and smooth muscle actin. Of the remaining 10 cases, three were not analyzable, and seven had normal karyotypes, although random structural changes were seen in two of them.