Meaningful assessment of a treatment modality for osteonecrosis (ON) must take into account a number of factors: (1) an accurate diagnosis, (2) consistent staging of the disease process, (3) understanding of the variability of the disease, (4) consistent application of the treatment modality (or the surgical technique), and (5) a clear understanding of the goal of the treatment used. This article reviews the important steps of a diagnostic algorithm that has been used to accurately diagnose and stage the disease process of ON. A consistent surgical technique with clearly defined goals is also outlined. The results of two clinical studies that were based on these diagnostic and therapeutic philosophies and that assess the role of core decompression in the treatment of ON are reviewed. The first study compared core decompression to conservative management in a prospective randomized study of 55 hips. Decompression provided more predictable pain relief and changed the indications for further surgical intervention more consistently than did conservative management. The second study represents a preliminary review of a ten-year study of the decompression procedure; it showed that core decompression was particularly useful in Stage I and Stage II ON. Roentgenographic stabilization was most predictable for Stage I hips. Core decompression can be a safe, effective, and predictable procedure in the treatment of Stage I and Stage II ON.