The authors try to identify causes of delay in the diagnosis of lung cancer, such causes being liable for low survival rates in five years. With this in mind, they developed a prospective study involving 100 patients admitted to the "Arnaldo Vieira de Carvalho" Cancer Institute, who were asked as to the date symptoms started, medical care searched, first diagnostic impressions, and number of physicians seen till the moment of diagnosis. They observed that 73 patients looked for medical assistance up to the 30th day from the beginning of disease, and only in 10 occasions this interval was longer than 120 days. 46 patients had a confirmed diagnosis in less than 90 days after their first medical appointment, and in 41 cases the delay in diagnosis was longer than 4 months. Upon the first exam with the physician, neoplasia was suspected 25 times, but only 11 patients were immediately referred to the Cancer Institute. Of the remaining 89 patients, 57 were referred only after their third medical appointment. 80 patients were first seen by general practitioners and, on average, patients went to 3 or 4 physicians to obtain a definite diagnosis. The most commonly used method to identify neoplasia was bronchofibroscopy (67 cases), with an average of 20 days of delay for its performance. Lung biopsy using transparietal fine needle was the second most used (14 cases), with an average delay of 10 days. The authors conclude that delay in the diagnosis is mostly due to the inadequacy of medical services, delay in referrals and in the performance of subsidiary tests.(ABSTRACT TRUNCATED AT 250 WORDS)