Our aim was to describe the MRI characteristics of septic and nonseptic olecranon bursitis. MRI contrast-enhanced examinations (n = 19) of 35 patients with olecranon bursitis (septic, n = 14; nonseptic, n = 21) were jointly reviewed by two musculoskeletal radiologists. We evaluated bursa size, extent of marginal lobulation, septation, concomitant elbow joint effusion, soft-tissue edema, rim enhancement, soft-tissue enhancement, degree of fluid complexity, definition of bursa margins, presence of edema, thickening of the triceps tendon, and bone marrow edema. Comparison of septic and nonseptic bursitis yielded the following results: marginal lobulation, 79% (11/14) versus 48% (10/21), p = 0.14; bursa septation, 64% (9/14) versus 57% (12/21), p = 1.0; moderate or marked complexity of bursa fluid, 64% (9/14) versus 29% (6/21), p = 0.15; poorly defined margins, 64% (9/14) versus 67% (14/21), p = 1.0; elbow joint effusion, 86% (12/14) versus 52% (11/21), p = 0.12; moderate to marked soft-tissue edema, 64% (9/14) versus 33% (7/21), p = 0.1; edema of the triceps, 57% (8/14) versus 48% (10/21), p = 0.73; thickening of the triceps, 43% (6/14) versus 14% (3/21), p = 0.21; bone marrow edema, 29% (4/14) versus 5% (1/21), p = 0.13; rim enhancement, 100% (11/11) versus 75% (6/8), p = 0.31; soft-tissue enhancement, 100% (11/11) versus 63% (5/8), p = 0.1. Septic and nonseptic olecranon bursitis present with a considerable overlap of MRI findings without statistically significant differences. Septic olecranon bursitis can be excluded in the absence of bursal and soft-tissue enhancement.