Anterosuperior instability of the shoulder may occur from a variety of pathologic lesions. We describe a specific entity, the SLAC (superior labrum, anterior cuff) lesion that involves an association of anterior-superior labral tear with a partial supraspinatus tear. We retrospectively isolated a group of 40 patients with this lesion. The presenting complaints, physical examination findings, surgical findings, and results were isolated. Overhead activities were the most common etiology; load and shift instability testing and whipple rotator cuff testing were the most common physical examination findings. Surgical repair was successful in 37 of the 40 patients. The SLAC lesion is a definable clinical entity with predictable history, examination, surgical pathology, and satisfactory results from surgery.