OBJECTIVES: To estimate the incidence and cost of LC in the US managed care population and determine if patient characteristics affect the ratio of LC performed in inpatients versus outpatients. METHODS: MEDSTAT MarketScanTM Commercial Claims and Encounters Database (CCED) contains inpatient (IP) and outpatient (OP) claims from over 2.5m people in 45 large U.S. employer-sponsored plans and recorded 366,674 adult IP admissions in 1999-2000. LC procedures were identified by ICD-9-CM and CPT-4 codes. Annual LC incidence rate was determined by percentage of persons age 18-65 undergoing LC within the average total CCED population in 1999-2000. Proportion of IP LC among all admissions was estimated. Proportions of IP and OP LC for all patients and by age, gender, and primary diagnosis were determined and compared by chi-square or Wilcoxon tests. Cost of LC was estimated within study groups. RESULTS: We identified 22,598 LC patients (IP 21.4%; OP 78.6%). Average annual LC incidence rate was 0.85%. Approximately 1.32% of all hospital admissions were for LC. 76.65% of LC patients were female. IP proportion was significantly higher in males than females (25.7% vs. 20.0%, p<0.001). Overall mean age was 45.84 (IP 46.64; OP 45.62, p<0.001). Proportion of IP among all LCs was significantly higher among older people (18-34y: 20.4%; 35-44y: 19.9%; 45-54y: 20.2%; 55-65y: 24.7%, p<0.001). IP proportions by diagnosis were: calculus of the gall bladder and/or bile duct, 31.8%; other gall bladder disorders (including cholecystitis), 13.9%; diseases of the pancreas, 87.6%; and all other diagnoses, 41.3% (p<0.001). Mean net cost for LC hospital admission was $9168 (95%CI: $8913-$9424) and average LOS was 3.6 days (95%CI: 3.4-3.8). Net OP procedure cost for LC was $3158 (95%CI: $3123-$3194). CONCLUSIONS: Nearly 80% of LCs in the US managed care population were ambulatory-based. Patients undergoing IP LC were significantly different from patients undergoing OP LC in age, gender, and primary diagnosis. Cost of hospital-based LC was almost three times higher than cost of ambulatory-based LC.