OBJECTIVES: The aim of this study is to evaluate the access of patients with lung cancer in a densely populated area of São Paulo to the Brazilian Public Health System, focusing on the time spent from symptom onset or initial diagnosis until the beginning of treatment. METHODS: We retrospectively reviewed 509 patients with malignant lung neoplasms who were admitted to a single reference oncology center of the public health system between July 2008 and December 2014. Patients were considered eligible for this study if they were older than 18 years and had not undergone any previous oncology treatment when they were admitted to the institution. The following data were collected from all patients: age, gender, smoking status, tumor staging, time from the when the first symptoms were experienced by the patient to when the patient was diagnosed with cancer, time from the first appointment to cancer diagnosis, and time from when the patient was diagnosed with cancer to the initiation of treatment. RESULTS: The median time from symptom onset to diagnosis was three months. From the first appointment to diagnosis, the median time interval was one month; however, 79% of patients were diagnosed in up to two months. The median time from diagnosis to the start of treatment was one month, but most patients (82.5%) started treatment in up to two months. CONCLUSION: In our highly populated region with preferential access to the public health system, patients are required to wait a relatively long time to effectively begin treatment for lung cancer. This type of study is important to alert medical societies and government health agencies.