OBJECTIVES: SCLC is estimated to represent 10-20% of lung cancer cases, however, the lack of specific ICD-9 diagnosis codes to differentiate SCLC and NSCLC poses challenges in claims data research. This study aims to (1) develop a definitional algorithm to identify SCLC in a large claims database, and to (2) assess payer costs associated with IV chemotherapy in SCLC. METHODS: Using medical claims data from 5.5 million beneficiaries between 01/01/1998 and 01/31/2006, we identified 8605 patients with lung cancer (ICD-9 codes 162.3-162.9, 176.4, or 197.0) receiving IV chemotherapies. We then identified SCLC by the following chemotherapies principally used for SCLC: cisplatin/etoposide, cisplatin/irinotecan, carboplatin/etoposide (aged 60 and over), or topotecan. We further limited this subset to exclude patients receiving treatments or procedures often associated with NSCLC: PET scan imaging, lung removal or resection surgery, and the regimen of carboplatin/paclitaxel. We computed average total costs paid per day of IV chemotherapy as well as the separate costs for IV chemotherapy drugs, IV chemotherapy administration procedures, and other drugs and services received on those days. RESULTS: A total of 1254 (14.6%) of patients with lung cancer had received a SCLC chemotherapy regimen, and the subset decreased to 942 (10.9%) when applying all exclusion criteria. Among the identified subset, average total cost per day was $815, with $423 (52%) attributable to IV chemotherapy drugs, $89 (11%) to IV chemotherapy administration procedures, and $303 (37%) to other drugs and services. CONCLUSION: The proposed algorithm identified about 11% of all patients with lung cancer as SCLC from claims data, a proportion comparable to published estimates. IV chemotherapy administration procedures and other visit-related drugs and services accounted for 48% of total costs per IV visit in these patients. The increased availability and use of oral chemotherapies in SCLC could provide savings to payers by offsetting some of these costs.