INTRODUCTION: People who inject drugs (PWID) are vulnerable to a range of harms, including vascular conditions such as chronic venous insufficiency (CVI), leg ulcers and deep vein thrombosis (DVT). The extent of vascular conditions has rarely been studied, despite contributing to considerable illness and disability among PWID. We assess the prevalence and associations of vascular conditions in PWID in London, UK. METHODS: Survey data from the community-recruited Care and Prevent Study of PWID in London were analysed. Participants were asked about CVI and leg ulcers using pictorial questions, and if they had ever been diagnosed with DVT. Associations between vascular conditions and demographic/drug-use information were explored using univariate and multivariable logistic regression. RESULTS: Among participants (n = 455), the prevalence of CVI, leg ulcers and DVT was 13% (n = 57), 10% (n = 46) and 23% (n = 105), respectively. CVI and DVT were positively associated with injecting into the groin, while injecting into the leg was positively associated with leg ulcers and DVT. CVI was also associated with not cleaning injection sites and diagnosed hepatitis C virus, and DVT with hepatitis C virus. DISCUSSION AND CONCLUSION: The prevalence of vascular problems among PWID in London is very high in comparison to the general population. These conditions are primarily associated with injection into the femoral vein. Use of these injection sites indicates peripheral venous access problems. There is a need to reinvigorate safe injection information provision in harm reduction services, with attention to reducing risk practices associated with venous damage and transitions to femoral injection.