A retrospective analysis was done of the records and radiographs of 100 club feet (in sixty-six patients) that had been consecutively treated with an operation. Twenty-six feet (26 per cent) had had a Grade-II deformity of the calcaneocuboid joint, as determined with a radiographic classification that had been developed on the basis of the degree of medial displacement of the cuboid. When the calcaneocuboid joint is in normal alignment, the central point of the cuboid ossification center lies on the mid-longitudinal axis of the calcaneus; when there is a Grade-I deformity, the mid-point of the cuboid ossification center lies lateral to the medial tangent but medial to the longitudinal axis of the calcaneus; and when there is a Grade-II deformity, the central point of the cuboid lies on or medial to the medial tangent of the calcaneus. Although a Grade-I deformity of the calcaneocuboid joint need not be corrected, a Grade-II deformity should be treated with release of the calcaneocuboid joint, which in this series was performed in conjunction with a complete subtalar release (including a talonavicular release). Sixteen of the twenty-six feet that had a Grade-II deformity had a complete release of the calcaneocuboid joint at the time of the operation; the release was not done in the remaining ten feet, some of which were operated on early in the series, before the importance of the deformity at the calcaneocuboid joint had been recognized.(ABSTRACT TRUNCATED AT 250 WORDS)