The prognostic significance of serum ferritin on survival in lung cancer was evaluated. One hundred and ninety-seven patients were referred for evaluation of pulmonary lesions; 115 patients (85 men) had primary lung cancer. Their median age was 57 years. Seventy-four patients (43 men) with benign lung disease were enrolled as controls. Their median age was 53 years. Serum ferritin was measured at diagnosis. Non-small cell lung cancer (NSCLC) (n=90) was graded according to the TNM-system and small cell lung cancer (SCLC) (n=25) in limited and extensive disease. Follow-up was median 30 months (range 23-36). Patients with lung cancer had higher median ferritin than controls (245 vs. 145 mug/l, p <0.00001): the prevalence of ferritin > 300 mug/l was 37% in patients with lung cancer and 14% in controls (p <0.001). There was no significant difference in ferritin between patients with different stages either in NSCLC or in SCLC. Patients with SCLC had higher median ferritin than patients with NSCLC (344 vs. 233 mug/l, p <0.05). No significant differences in ferritin could be demonstrated among the other histological tumour types. The overall survival rate in patients with lung cancer was 52% after 1 year, 33% after 2 years, and 13% after 3 years. Survival rate was lower in patients with ferritin > 300 mug/l than in those with ferritin less than or equal to 300 mug/l (p <0.0001). The probability of survival 1, 2 and 3 years after diagnosis in patients with ferritin > 300 mug/l was 36, 20 and 4%, respectively, and in patients with ferritin less than or equal to 300 it was 63, 42 and 18%, respectively (p <0.0001). An elevated ferritin was a significant prognostic factor (p <0.01) even after adjustment for performance status, age, sex, TNM stage, and histological tumour type. TNM stage and performance status were likewise predictors of survival (p <0.01 and p <0.001, respectively). There exists a clinically relevant relationship between serum ferritin concentration and the prognosis of survival in patients with primary lung cancer. The routine use of serum ferritin should be considered in the evaluation and follow-up of pulmonary malignancies.