OBJECTIVE. The objective of the present study is to evaluate arthritis-like findings on MRI studies of the forefeet of healthy volunteers versus patients with symptomatic rheumatoid arthritis (RA) or psoriatic arthritis (PsA). MATERIALS AND METHODS. Two observers analyzed MR images of the forefeet of 31 healthy volunteers, 30 patients with symptomatic RA, and 30 patients with symptomatic PsA, to identify MRI patterns of RA or PsA (e.g., bone marrow edema [BME], erosions, tenosynovitis, joint effusion, periarticular soft-tissue edema, or bony proliferations) on the basis of the Outcome Measures in Rheumatoid Arthritis Clinical Trial RA MRI scoring system and the PsA MRI scoring system. The Mann-Whitney test with Bonferroni correction was used for statistical analysis. RESULTS. Reader 1 found BME in 14 healthy volunteers (45%), whereas reader 2 found BME in 10 volunteers (32%). Tenosynovitis was observed by reader 1 in three healthy volunteers (10%). Joint effusion was found by reader 1 in seven healthy volunteers (23%) and by reader 2 in three volunteers (10%); the mean intensity grades for these findings were low (range, 1-1.33). Erosions, soft-tissue edema, and bony proliferations were not found in the forefeet of healthy volunteers. Reader 1 and reader 2 observed all arthritis-like features on the MR images of patients with RA. The percentages of patients with RA who had such MRI features, as identified by reader 1 and reader 2, respectively, were as follows: BME, 83% and 80%; erosions, 40% and 40%; tenosynovitis, 33% and 17%; effusion, 87% and 53%; soft-tissue edema, 20% and 27%; and bony proliferations, 3% and 3%. The percentages of patients with PsA who were found to have arthritis-like findings on MR images, as determined by reader 1 and reader 2, respectively, were as follows: BME, 70% and 67%; erosions, 20% and 20%; tenosynovitis, 57% and 50%; effusion, 70% and 37%; and soft-tissue edema, 60% and 53%. Bony proliferations were observed by reader 2 only in 7% of patients with PsA. The mean minimum intensity grade was 1 (for tenosynovitis in patients with RA, as observed by reader 2), whereas the maximum intensity grade was 2.53 (for erosions in patients with RA, as observed by reader 1). Tenosynovitis and soft-tissue edema were observed more frequently in patients with PsA than in patients with RA (p = 0.001-0.059). CONCLUSION. On the forefoot of healthy volunteers, mild BME is a common finding, and tenosynovitis and joint effusion are occasional findings. The frequency and intensity of arthritis-like findings on MRI are similar in patients with RA and PsA, with the exception of tenosynovitis and soft-tissue edema, which are more frequently observed in patients with PsA than in patients with RA.