There is relatively little research specifically investigating patellofemoral joint osteoarthritis (PFJ OA). In particular, the source of pain in PFJ OA has not been established. One structure that may be an important contributor is the infrapatellar fat pad (IPFP). This cross-sectional study aimed to: (1) compare IPFP volume in individuals with and without PFJ OA and (2) assess the relationship between IPFP volume and pain in individuals with PFJ OA. Thirty-five participants with symptomatic and radiographic PFJ OA and 11 asymptomatic controls with no radiographic signs of OA were recruited. IPFP volume was measured in both groups from magnetic resonance images, and pain in the PFJ OA group was determined using the pain subscale of the Knee Injury and Osteoarthritis Outcome Score (KOOS-pain). The PFJ OA group had 23.6 % greater IPFP volume than the control group (p = 0.04). After the inclusion of covariates, IPFP volume remained 19.6 % greater in the PFJ OA group (p = 0.03). IPFP volume explained 20.1 % of the variance in KOOS-pain in the PFJ OA group, with a larger IPFP being associated with worse pain (p < 0.01). Individuals with PFJ OA had a larger IPFP than controls, and IPFP volume was directly related to PFJ OA pain. These data suggest a role for the IPFP in PFJ OA and highlight a need for further investigation into the casual relationship between IPFP and PFJ changes.