Initially, a physician obtains a patient's medical history, including any tobacco use, smoke exposure and family hsitory of cancer. The physician will conduct a physical examination of the patient's body for signs of disease and other health problems.

Imaging tests, which use x-rays, magnetic fields or radioactive substances (e.g., CAT scans, MRIs, PET scans) are often used to create a picture of the body.

Other tests that may be used to diagnose SCLC include blood and urine tests, which can identify chemical or hormonal abnormalities suggestive of cancer, or sputum cytology tests. In this test, a sample of sputum or phlegm is taken for microscopic examination. At times, this test has led to early detection of carcinomas.

A biopsy sample is usually taken and viewed under a microscope to confirm a suspected diagnosis of small cell lung cancer. Samples may be obtained by a number of procedures, including bronchoscopy, mediastinoscopy, needle biopsy and others. Abiopsy can determine the type and stage of the cancer, which is used for treatment planning and prognosis.