Primary cutaneous adenoid cystic carcinoma of the eyelid is an extremely rare entity with the propensity to recur locally, spread to regional lymph nodes, and invade perineural spaces. Of the 8 cases previously reported in the literature, only 2 were noted to be associated with perineural invasion, and neither of these was treated with radiation therapy. The authors report the case of a 35-year-old woman who presented with a progressively enlarging left lower eyelid lesion. An excisional biopsy with wide margins revealed a diagnosis of primary adenoid cystic carcinoma of the eyelid with perineural invasion. Because of the high risk of recurrence associated with perineural invasion, the patient received postoperative adjuvant radiation in the form of 50 Gy relative biological effectiveness of proton beam therapy to the postoperative tumor bed and to the infraorbital nerve tracking back to the apex of the orbit, followed by a 10-Gy boost to the lower eyelid tumor bed with orthovoltage x-rays.