Consideration of sentinel lymph node biopsy (SLNB) is recommended for thin melanomas with poor prognostic features; however, few metastases are identified. The purpose of this study was to assess the cost effectiveness of SLNB in this population.The prospective melanoma database was reviewed to identify patients with melanomas1.2 mm thick who had undergone SLNB. Physician and hospital charges were collected from the appropriate billing department.A total of 138 patients were identified over an 8-year period (1994-2002). Two patients with positive SLNs were identified (1.4%), one with a melanoma1 mm thick. Patient charges for SLNB ranged from $10,096 to $15,223 US dollars, compared with $1000 to $1740 US dollars for wide excision as an outpatient. Using these charges, the cost to identify a single positive SLN would be between $696,600 and $1,051,100 US dollars. The cost for wide excision would be between $69,000 and $120,100 US dollars. Assuming that all patients with a positive SLN would die of melanoma, the cost per life saved would be $627,000 to $931,000 US dollars.The cost of performing SLNB in this population is great and only a small number will have disease identified that will alter treatment. These data call into question the appropriateness of SLNB for thin melanomas.