Unicameral bone cysts are rare in adults and are most often found incidentally on radiographs. However, they can persist from the adolescent period and may be present in locations that predispose to or exacerbate fractures.This article describes a case of a healthy 40-year-old woman who sustained a proximal humerus trauma that involved a large unicameral bone cyst, resulting in a 3-part head-splitting fracture. The epiphyseal location of the cyst contributed to the severity and extent of the fracture that resulted from a simple fall. Given the age of the patient, open reduction and internal fixation with a locking plate and lag screws was performed. The patient chose open reduction and internal fixation to preserve a hemiarthroplasty procedure in case of future revision. Successful humeral head reconstruction was achieved, and the patient fully recovered. One year postoperatively, the patient underwent arthroscopic debridement to alleviate subjective stiffness and decreased range of motion.Multipart head-splitting fractures require complex repair strategies. The gold standard for the treatment of these injuries is hemiarthroplasty. However, the decision process is difficult in a young patient given the average survival of autoplastic prostheses and the added difficulty of later revision. The current case demonstrates the complexity of decision making resulting from a rare injury in a young, healthy patient and shows that open reduction and internal fixation can provide acceptable reconstruction in such situations.