OBJECTIVES: We aimed to clarify the clinical implication of ultrasound (US)-detected foot joint inflammation in tightly controlled patients with rheumatoid arthritis (RA). METHODS: We evaluated bilateral foot joints (second to fifth metatarsophalangeal joints of forefoot; tarsometatarsal, cuneonavicular and midtarsal joints of midfoot) of 430 RA patients for synovitis using Power Doppler (PD) imaging by US. We made a cross-sectional and a 3-year longitudinal analysis about the associations of US-detected synovitis with clinical, laboratory and radiographic data as well as foot-specific outcomes using a self-administered foot evaluation questionnaire (SAFE-Q). RESULTS: The US-detected foot synovitis was seen in 28% of patients. The US-detected synovitis was closely related to 28 joint-disease activity score (DAS28) more in the forefoot than in the midfoot, while related to joint destruction in both. Multiple regression analyses showed significant associations between midfoot PD positivity and SAFE-Q in the remission group. SAFE-Q was worsened after the 3-year interval, but PD positivity at baseline did not contribute to the changes. On the other hand, destruction of the joints with US-detected synovitis significantly progressed in 3 years than with not. CONCLUSIONS: US-detected synovitis on foot joints were related to systemic inflammation, clinical symptoms, and future joint destruction with region specificity.