Objective: To assess physician, patient, and skin lesion characteristics that affect the number of benign skin lesions excised by primary care physicians for each skin cancer. Design: Prospective study collecting clinical, patient, and histopathologic details of excisions or biopsies of skin lesions by random samples of primary care physicians. Setting: Southeast Queensland involving traditional family medicine physicians (n=104; response rate,53.9%) and family medicine physicians working in 27 primary care skin cancer clinics (n=50; response rate,75.0%). Participants: Of 28 755 skin examinations recorded during the study, 11 403 skin lesions were excised or biopsied; 97.5% of the excised lesions had clinical and histologic diagnoses recorded. Main Outcome Measures: Number of lesions needed to excise or biopsy (NNE) for 1 melanoma (pigmented lesions only) and NNE for 1 nonmelanoma skin cancer (nonpigmented lesions only). Results: The NNE for nonpigmented lesions (n=8139) was 1.5 (95% confidence interval, 1.4-1.6) and for pigmented lesions (n=2977) was 19.6 (16.2-22.9). The NNE estimates were up to 8 times lower if the physician thought the lesion was likely to be malignant and up to 2.5 times higher if there was strong patient pressure to excise. The NNE estimates varied by other physician-, patient-, and lesion-related variables. Conclusions: Clinical impressions of excised skin lesions were strongly associated with NNE estimates. By focusing on pigmented skin lesions and by addressing the physician- and patient-specific factors identified, the effectiveness of future training for primary care physicians in the clinical management of skin cancer could be improved.