JOHN B. KANEENE, DVM, MPH, PhD 1 , ULREH V. MOSTOSKY, DVM, MS 1 , and ROSEANN MILLER, MS 1 1 Center for Comparative Epidemiology and the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824-1314 Vet Surg April 2009 38 3 398-405 Objective—To determine whether there has been improvement in canine hip joint phenotype classifications of dogs whelped from 1989 to 2003 by the Orthopedic Foundation for Animals (OFA), by examining results of radiographic evaluations and identifying any trends in percentages of dogs classified as having desirable hip joint phenotypes. Study Design—Retrospective cohort study. Sample Population—OFA radiographic classifications (n=431,483) on dogs whelped between 1989 and 2003. Methods—Numbers and percentages of dogs classified by hip joint phenotypes were determined for 2-year cohorts. Differences between breeds and sexes were assessed using the Fisher's exact test, and odds ratios with 95% confidence intervals were calculated to express associations. The Cochran–Armitage test for trend was calculated to identify significant trends over time. Results—There were statistically significant (P<.05) increases in the proportion of all breeds of dogs evaluated as excellent and good from 1993 to 2003, controlling for gender and age at evaluation. Labrador Retrievers, Bernese Mountain Dogs, and Rottweilers had the highest proportions of excellent and good scores, and the highest rates of improvement in excellent and good scores were seen in Bernese Mountain Dogs and Rottweilers. Conclusions—Results support the contention that there have been improvements in hip joint phenotype classifications in dogs in the United States since the previous study (1989–1992), through increases in the proportion of dogs receiving excellent and good classifications. Clinical Relevance—Hip joint phenotype classifications can be used by dog breeders to develop breeding programs to improve the hip joints of future generations of dogs.