A five-year follow-up study of prognostic factors in 207 patients with squamous cell lung cancer (SqLC) radically treated with surgery was investigated. Cellular prognostic indicators for survival times, such as percentage of cells in the S-phase (S-phase fraction, SPF), proliferative index (PI, number of cells in S + G2/M phases) and DNA ploidy, in addition to well known clinical factors were studied. Patients with aneuploid tumours had significantly shorter survival period (P < 0.05) than patients with diploid tumours. However, proliferative rate of the tumours had no influence on patients' survival. Cox multivariate analysis showed that metastases to the neighbouring lymph nodes, tumour diameter > 5 cm and DNA aneuploidy of the tumour cells were the negative factors which affected patients survival. DNA ploidy did not depend on the clinical stage of the tumours.