Abstract Objective To present the findings of all patients with periocular basal cell carcinoma (BCC) treated with Mohs' micrographic surgery (MMS) in Australia between 1993 and 1999. Design Prospective, noncomparative, multicenter, interventional case series. Methods Prospective series of 1295 patients undergoing MMS for periocular BCC over a 7-year period (1993–1999). Inclusion criteria Periocular BCC referred for MMS. Main outcome measures Site, tumor size, prior occurrence, defect size, histologic subtype, and presence of perineural invasion. Results Twelve hundred ninety-five patients had 615 (47.5%) lower eyelid, 626 (48.3%) medial canthus, and 51 (3.9%) upper eyelid BCCs. The most common histologic subtypes were nodulocystic (39.5%) and infiltrating (34.8%) ( P = 0.0008). Sixty-eight percent were primary and 32% were recurrent tumors. Previously recurrent BCCs were larger ( P<0.0001), with larger defects ( P<0.0001) than primary BCCs, and had more subclinical extension ( P<0.0001) requiring more levels for complete excision ( P<0.0001). Furthermore, superficial BCCs were more likely to have a prior occurrence ( P<0.0001). In this series, perineural invasion was found in 1% of cases, with greater subclinical tumor extension in such cases ( P = 0.0657). Conclusion The Australian MMS database is the largest prospective, nationwide series of high-risk periocular BCC managed by MMS. Almost 50% of tumors were at the medial canthus, with nodulocystic and infiltrating being the most common histologic subtypes. Recurrent BCCs comprised a third of tumors and were larger, with larger defects and more subclinical extension than primary BCCs. Perineural invasion was found in 1% of cases and also had greater subclinical extension.