The authors report on a consecutive series of 253 cases of seminoma of the testis followed with periodic chest X-ray examinations from a minimum of three to a maximum of 27 years. The detection rate of asymptomatic intrathoracic metastases (ITM) was considered together with the costs of the follow-up procedure. Chest X-ray follow-up is not advisable beyond one year from primary treatment, since most (14 of 18) ITM occur in the first year, the detection rate of ITM beyond this date is too low (0.11% patients/year), and the related costs are too high (over $130,000 per ITM detected). Chest X-ray follow-up is questionable even in the first year after primary treatment for Stage I cases because of the low detection rate (1.38% patients/year) and the high costs (over $14,000 per ITM detected), whereas it appears to be opportune in Stages IIA and IIB.