Purpose: Knee pain is a common symptom experienced by patients of all ages and sexes. Though the underlying pathologies are numerous, one of the most common causes of knee pain, especially in the aging population, is osteoarthritis (OA). OA is associated with significant disability, morbidity and mortality. In contrast, the burden of knee pain and its association with chronic disease is not well understood, though joint pain has been previously suggested to adversely impact outcomes in patients with multiple co-morbidities. This study therefore seeks to understand the relationship of knee pain, with and without associated OA, and the prevalence of common chronic conditions in primary care populations within Southwestern Ontario. Methods: In Southwestern Ontario, the Deliver Primary Health Care Information (DELPHI) database has been developed to share primary health information with researchers. The data presented in this study is a retrospective analysis of International Classification of Primary Care (ICPC-2R) coded encounters in the DELPHI database. This database contains data from 1790 patients under the care of 23 physicians encompassing 15,149 randomly selected encounters between 2006-2010. According to the ICPC-2R coding, L15 represents knee symptom/knee complaint and L90 is the diagnostic code for OA. Results: Between 2006 and 2010, 209/1790 (11.7%) patients presented with knee symptoms/knee complaint (L15) in a total of 342 visits. Of these 209 patients, 99 (60 females, 39 males) had a diagnosis of osteoarthritis (L90) while 110 (60 females, 50 males) did not. Of the 99 patients with OA, 64 of these were new diagnoses made within the study period and 57 of them were diagnosed at their first L15 visit. Using chi-square analysis and pairwise comparison of proportions, we found statistically significant increases in the prevalence of diabetes (13.6% versus 20.9% with L15, p=.004), hypertension (28.1% versus 45.5% with L15, p<.001) and heart failure (3.5% versus 8.2% with L15, p=.013) in patients with knee symptoms/complaints without OA compared to the prevalence within the study population. Additionally, we saw modest (but not significant) increases in the prevalence of depression and anxiety (19.6% versus 28.2% with L15), hyperlipidemia (15.7% versus 22.7% with L15), obesity (7.5% versus 8.2% with L15) and osteoporosis (5.2% versus 6.4% L15) in patients with knee symptoms/complaints without OA compared to the prevalence within the study population. Interestingly, in patients with OA experiencing persistent knee symptoms/complaints we see a higher prevalence of diabetes (23.2%), hypertension (54.5%), hyperlipidemia (24.2%), obesity (14.1%), osteoporosis (10.1%) compared to those with knee symptoms alone. In patients with OA and persistent knee symptoms/complaints we see depression and anxiety (23.2%) and heart failure (5.1%) with reduced prevalence compared to what was seen in patients with knee symptoms/complaints alone. Conclusions: Our data show that knee pain is a common presenting complaint in the primary care population and OA is identified to be the cause of that symptom in approximately 48.8% of these cases. Our data support previous findings that suggest knee OA is a common contributor to multi-morbidity and an increasingly prevalent challenge to healthcare. Interestingly however, our data also show that knee pain alone, without OA, is also associated with significant increases in the prevalence of these same conditions when compared to the general study population. Furthermore, increases in the prevalence of depression, anxiety and heart failure are also seen in patients with isolated knee pain without OA. These findings can help primary care physicians better understand the population of patients presenting with knee pain and improve our understanding of the burden of the symptom, with or without OA as the underlying cause. Furthermore, understanding the relationship between chronic disease, mental health and pain can help guide multimodal management strategies to comprehensively manage symptoms, despite limited disease modifying strategies available for OA.