Adventitial (adventitious) bursae occur as a pathological condition in areas between soft tissues and bone where abnormal friction arises due to professional, traumatic, or sport activity. An atypical localization of an adventitial bursa was noticed on the ulnar margin of the distal forearm in a woman with a mild bone misalignment, as a professional disorder. The clinical presentation was one of subcutaneous mass with mild pain and no local signs of inflammation. A 1-year follow-up visit noted the degeneration of the bursa into a cystic lesion, as proved with a grayscale sonogram, using a 14 MHz linear transducer. This was an unexpected chronic evolution. A quick literature search found either resolution or a chronic course with complications as fibrosis, infection, and ulceration of adventitial bursitis.