OBJECTIVES:  Lapatinib is an oral dual tyrosine kinase inhibitor that has been shown to improve time to progression when combined with capecitabine versus capecitabine monotherapy in women with HER2+ MBC previously treated with trastuzumab. Data on health care utilization and costs among women receiving lapatinib in typical clinical practice are scarce. METHODS:  This was retrospective observational descriptive study of health care utilization and costs among women receiving lapatinib after treatment with trastuzumab for MBC in the Thomson MedStat MarketScan Commercial and Medicare health insurance claims databases (1/2000-3/2010). Monthly utilization and costs were calculated for the 12 months prior to initiation of lapatinib (pre-treatment period), the lapatinib treatment period, and the post-treatment period (end of lapatinib treatment to end of study/disenrollment). RESULTS:  Mean (SD) age was 52(8) and 72(6) years in Commercial (n=572) and Medicare (n=94) patients respectively. Lapatinib was initiated in combination w/capecitabine in 63% and w/trastuzumab in 22% of patients. Median time to lapatinib discontinuation was 7.4 months. The mean(SD) number of visits/month declined from 6.1(3.0) during pre-treatment to 5.5(3.5) during treatment, and to 4.6(3.9) during post-treatment. The mean(SD) number of inpatient days/month increased progressively from 0.24(0.52) during pre-treatment, to 0.53(1.39) during treatment and 0.96(2.52) post-treatment. Mean(SD) lapatinib costs/month during treatment were $2,097($877). Mean(SD) trastuzumab costs/month were $2,762($2,020), $722($1,731), and $1,166($2,134) during pre-treatment, treatment, and post-treatment, respectively. Corresponding mean(SD) chemotherapy costs/month were $1,355($1,898), $1,496($1,698), and $1,437($2,729), respectively, while corresponding mean(SD) chemotherapy administration costs/month were $508($477), $189($289), and $326($516) respectively. Mean(SD) other (including inpatient) costs/month were $5,446($4,680), $5,564($7,198), and $6,880($9,726), respectively. Mean(SD) total costs/month were $10,071($6,056), $10,067($7,695), and $9,809($10,853), respectively. CONCLUSIONS:  In this sample of women receiving lapatinib after treatment with trastuzumab for MBC, monthly health care costs were similar during lapatinib treatment versus prior to treatment, despite progressively increasing inpatient utilization and costs, potentially reflecting disease progression over time.