In this review, we discuss mucoid cysts, which are common benign cysts, most often located dorsally or laterally to the distal interphalangeal joint. The origin of the cyst is suggested to be similar to that of a ganglion, or to be a degeneration of dermis, and it is often linked to osteoarthritis. Two types of mucoid cysts seem to exist, probably needing different treatment. A cyst is usually asymptomatic and needs no treatment, but limited joint movement, pain and nail deformity may occur. In the latter case, conservative or surgical treatment is asked for. If a cyst is atypical, pathology is needed.