We report two rare cases of adult-onset phalangeal microgeodic syndrome (PMS), which commonly develops in children. Both cases were Japanese women, with case 1: 60years old and case 2: 58years old. They developed swelling and stiffness in their fingers in winter, and their symptoms disappeared without any treatment in summer. Magnetic resonance imaging (MRI) of bilateral hands showed diffuse bone edema of the middle and proximal phalanges in winter, but the abnormal findings also disappeared in summer. The specific abnormalities observed on MRI were very useful for the diagnosis of PMS. Interestingly, they appeared in winter and disappeared in summer in parallel with the symptoms.