© 2016 World Federation for Ultrasound in Medicine & Biology.In this study, the best ultrasound (US) aspect for detection of fifth metatarsophalangeal (MTP) joint erosions, the most frequently eroded joint, in rheumatoid arthritis (RA) patients is investigated. Forty-eight RA patients (F/M = 35/13, mean age and disease durations 50.3 ± 11.8 and 7.9 ± 6.9 y, respectively) were evaluated by B-mode US for erosion. Images were obtained from the dorsal, lateral and plantar aspect of the fifth MTP joint, in longitudinal and transverse scans. The fifth MTP erosions were detected in 36 of 48 patients (75%) and 67 of 96 feet (69.8%). Of the erosions, 15 (22.4%), 53 (79.1%) and 59 (88.0%) were observed at dorsal, lateral and plantar aspects, respectively. Despite not being statistically different, the detection rate of fifth MTP erosions was numerically higher in the plantar aspect than both the lateral and dorsal aspects. In conclusion, the fifth MTP erosions in RA patients are more commonly detected in the plantar aspect US than in dorsal and lateral assessments.