Hip dysplasia is a common developmental problem affecting the canine population. Despite extensive research into the condition, many questions remain unanswered and numerous misconceptions are present among the general public. The purpose of this paper is to review the current knowledge on the development of hip dysplasia, factors modifying its development, and current diagnostic techniques.A computerized literature search was conducted for the period of January 1983 to April 1985 using the MEDLINE and CAB databases, and the keywords hip dysplasia, hip, dog, and canine. Other articles,wherever possible original research articles, published before 1983 were also reviewed. Animals affected by hip dysplasia are born with normal hips, but quickly develop subluxation of the femoral head. Degenerative joint disease follows. Hip dysplasia is a complex, inherited, polygenic trait. Selective breeding of only normal dogs with normal littermates, parents, and grandparents is there commended method of reducing the incidence in the general population.Gene expression in affected individuals may be modified by a number of environmental factors. These factors do not cause hip dysplasia, but they alter manifestations of the trait and its severity. Nutrition is a major environmental factor. Excess energy consumption increases the frequency and severity of hip dysplasia in genetically predisposed dogs. Food intake should be regulated to maintain a slender figure with the ribs and dorsal vertebral spines easily palpable, but not visible. Excess dietary calcium and vitamin D contribute to hip dysplasia in genetically predisposed individuals and should be avoided. High dose vitamin C supplementation ingrowing puppies does not prevent hip dysplasia, and this practice should be discontinued. Animals must be 2 years old before they can be certified as normal, but the disease may be diagnosed earlier. Earlier diagnosis of the condition would be very useful for the selection of breeding stock, but palpation techniques and the standard extended view radiographs have unacceptably high rates of error in young puppies. Stress radiography techniques may improve the accuracy of early diagnosis in the future.