To determine the prevalence of the primary glaucoma (PG) and occurrence of primary glaucoma in initially non-affected normal eye. Medical records of 7751 dogs presented to the Veterinary Medical Teaching Hospital (VMTH) of Seoul National University (SNU) between January 2006 and December 2009 were examined. Among 7751 dogs, forty three dogs (0.55%) developed PG. The following breeds were included in the study: 18 American Cocker Spaniels, 17 Shih Tzus, 3 Mixed Breeds, 2 Malteses, 2 Pekingeses, and 1 Chow Chow. The mean onset age of PG in the first eyes was $7.1{pm}2.3$ years in the all breeds. Compared with Mixed Breed (0.54%), American Cocker Spaniel (3.16%, p = 0.004) and Chow Chow (20%, p = 0.001) had a higher risk of developing glaucoma. Twenty six of 43 dogs (60.1%) were females with male-to-female ratio of 1:1.53. Twenty nine of 33 eyes (87.9%) developed glaucoma in the fellow eye within mean ${pm}SD$ time of $17.5{pm}2.7$ months. From this study, American Cocker Spaniel and Shih Tzu were the most frequent PG breed in Korea. Also, unilateral PG dogs developed glaucoma in the non-affected normal eye within approximately 17 months. The results indicate that prophylactic medical therapy with antiglaucoma agents should be considered to delay or prevent developing glaucoma in non-affected normal eye.