ObjectiveTo estimate the prevalence of erosive disease in 1st carpometacarpal joints (CMCJs) and investigate its clinical impact compared with radiographic thumb base (TB) osteoarthritis. Patient and methodsStandardised assessments with hand radiographs were performed in participants of two population-based cohort studies in North Staffordshire with hand symptoms lasting ≥1 day in the past month. Erosive disease was defined as the presence of eroded or remodelled phase in ≥1 interphalangeal joint (IPJ) or 1stCMCJ following the Verbruggen-Veys classification. Hand pain and function were assessed with AUSCAN. Prevalence was estimated by dividing the number of persons with erosive lesions by population size. Linear and logistic regression analyses were used to contrast clinical determinants between persons with erosions and with radiographic TB osteoarthritis. Results were presented as mean differences and odds ratios with 95% confidence intervals (95%CI), adjusted for age,sex and radiographic severity. Results1076 participants were studied (60% women, mean age 64.7 years (SD 8.3); 24 persons had erosive disease in the TB. The prevalence of erosive disease in 1stCMCJs was 2.2% (95%CI 1.4, 3.3). Only 0.5% (95%CI 0.2, 1.2) had erosive disease affecting IPJs and 1stCMCJs combined. More persons with erosive disease of 1st CMCJs reported pain in their TB than persons with radiographic TB osteoarthritis, AUSCAN pain and function scores were similar. ConclusionErosive disease of 1st CMCJs was present in 2.2% of subjects with hand pain and was often not accompanied by erosions in IPJs. Erosive disease was associated with TB pain, but not with the level of pain, when compared with radiographic TB osteoarthritis.