BACKGROUND:: The trochlear groove is the rarest location for osteochondritis dissecans (OCD) of the knee, with only about 50 previously reported cases, most of which were treated before the advent of magnetic resonance imaging (MRI) and modern techniques of cartilage fixation or osteochondral transplantation. The purpose of this multicenter study was to assess the patient presentation and clinical, radiographic, and functional results of treatment for trochlear groove OCD lesions. METHODS:: Hospital records from 5 institutions of the Research in Osteochondritis of the Knee (ROCK) study group were retrospectively reviewed for cases of trochlear groove OCD. Demographics, clinical presentation, diagnosis, treatment, time to pain resolution, and return to sports were recorded. Lesion appearance, size, stability, and time to radiographic healing were evaluated on plain x-rays and MRIs. RESULTS:: Trochlear groove OCD lesions were evaluated in 24 knees in 21 adolescents (17 male, 4 female), with an average age of 14 years (range, 10 to 18 y). Fifty-four percent (13/24) of the lesions were identifiable on radiographs, and all were identifiable on MRI, 38% of which (9/24) was unstable. One fourth (6/24) of knees had coexistent femoral condyle OCD lesions. Treatment outcomes were evaluated in patients with a minimum of 1-year follow-up (average: 3 y; range: 1 to 12 y) or healing before 1 year. Half of the knees (2/4) treated nonoperatively and two thirds (8/12) treated operatively showed radiographic signs of healing with patients returning to full activity without pain. Operative treatment success rates were as follows: drilling (3/3), fixation (3/3), microfracture (1/2), drilling with subsequent delayed microfracture (1/1), and drilling with fixation (0/3). CONCLUSIONS:: MRI aids in the diagnosis and staging of trochlear groove OCD lesions, as almost one half may not be identifiable on radiographs, and one quarter are associated with OCD lesions in other locations of the same knee. Multiple operative treatments can be used to achieve healing or resolution of symptoms in stable and unstable lesions; however, a larger comparative study is needed to make specific recommendations.