BACKGROUND: Sinonasal carcinomas, including nonkeratinizing (NK) squamous cell carcinoma (SCC) and sinonasal undifferentiated carcinoma (SNUC), are uncommon malignant neoplasms arising from the Schneiderian respiratory epithelium of the nasal cavity and paranasal sinuses. Due to their low frequency, the cytogenetic data on these tumors is limited. METHODS: Seventeen patients who were operated on in our institution for extirpation of paranasal carcinomas were enrolled in this study. Fourteen pathologically confirmed samples of sinonasal carcinomas were cytogenetically analyzed using G-banding techniques after short-term culture. Three samples did not grow on culture. RESULTS: Five of the 14 sinonasal carcinomas had an abnormal karyotype (36%). Of the 9 NK SCCs, 3 had abnormal karyotypes with numerical and structural chromosomal anomalies. Of the 5 patients with SNUC, 2 had an abnormal karyotype. One case of SNUC had a diploid complex karyotype. Another case of SNUC had a near triploid composite karyotype with 60-69 chromosomes. The chromosome arms that involved frequent breakpoint and rearrangements were: 1p, 6p, 7p, and 12q. We found that 3 of the 3 patients who died of disease displayed an abnormal karyotype, whereas 2 of the 11 patients who are alive displayed an abnormal karyotype (P = 0.027). CONCLUSIONS: The study revealed that more than a third of the paranasal carcinomas carry an abnormal karyotype. No specific common aberrations were found in these tumors. To our knowledge this is the first attempt to investigate sinonasal squamous and undifferentiated carcinomas on a genetic level using G-banding technique. Additional studies are required in order to determine whether cytogenetic data may serve as an adjunct to conventional pathology for the diagnosis and prognosis assessment of these rare and highly aggressive tumors.