Between 1973 and 1982 forty-six fractures of the base of the fifth metatarsal, distal to the tuberosity, were treated and followed for a mean of forty months (range, six to 108 months). Roentgenographic criteria were used to define three types of fractures: acute fractures characterized by a narrow fracture line and absence of intramedullary sclerosis; those with delayed union, with widening of the fracture line and evidence of intramedullary sclerosis; and those with non-union and complete obliteration of the medullary canal by sclerotic bone. Of the twenty-five acute fractures in this series, fifteen were treated with a non-weight-bearing toe-to-knee cast, and fourteen of them healed in a mean of seven weeks. Only four of the other ten, which were treated with various weight-bearing methods, progressed to union. Of the twelve patients with delayed union, one refused treatment, one was treated with a bone graft, and ten were treated initially by immobilization of the limb in a plaster cast and weight-bearing. Of these ten fractures, seven healed in a mean of 15.1 months and three eventually required grafting for non-union. Of the nine non-unions in the series, which were treated primarily with medullary curettage and bone-grafting, eight healed in a mean of three months. In all, twenty fractures were treated surgically with an autogenous corticocancellous graft that was inlaid after thorough curettage and drilling of the sclerotic bone that obliterated the intramedullary cavity. Of these twenty fractures, nineteen progressed to complete healing and one, to asymptomatic non-union.(ABSTRACT TRUNCATED AT 250 WORDS)