The prevalence and pattern of osteoarthritis of the knee and its association with obesity among security forces personnel was investigated. A single survey with a control group was done at the Mobile Hospital, Ministry of Interior, Makkah Al Mukarramah. One hundred twenty-five patients presenting to the orthopedic clinic with painful knees of at least 12 months duration gave detailed histories and were treated with bi-planar conventional radiography; they were matched with a similar number from the clinics of internal medicine without painful knees. One hundred three patients (82.4%) with 126 painful knees had various degrees of osteoarthritis. The mean age was 41 and 41.76 years for the patient and control group, respectively. The medial tibio-femoral and patello-femoral compartment were involved in 116 cases (92%). Fifty-nine knees (46.8%) had mild, 46 (36.5%) had moderate, and 21 (16.6%) had severe osteoarthritis changes. There were statistically significant differences between the two groups for weight and Quetelet index of body mass (p < 0.047 and < 0.0001). In the study group, the mean Quetelet body index was 31.6638 kg/m2, and in the control group it was 28.5633 kg/m2. The prevalence of osteoarthritis among the security forces personnel was 1.19%. The medial and patello-femoral compartment was affected in the majority of cases, and obesity was confirmed as one of the important causes of osteoarthritis in the Saudi Arabian population.