The widespread use of diagnostic radiography, especially using magnetic resonance imaging, has helped to increase the diagnosis of paralabral cysts in patients with chronic shoulder pain. These paralabral cysts are frequent in the anterior, the superior, and the posterior compartment of the shoulder joint but are rare in the inferior compartment. Paralabral cysts in the shoulder appear particularly in men in their third and fourth decades but rarely in elderly patients. We report a case of an inferior paralabral cyst in an elderly patient whom we treated through arthroscopic decompression. The increased use of diagnostic magnetic resonance imaging (MRI) in patients with chronic shoulder pain has correlated with the increase in the diagnosis of paralabral cysts. Paralabral cysts are commonly associated with labral or capsule tears through which synovial fluid seeps out into the extra-articular space; the labral or the capsule tear essentially becomes a 'one-wayvalve'.1,2) Paralabral cysts are present in 2% to 4% of the population, most of whom are 30-to 40-year-old men. They are rarely present in the elderly population. Generally, the cysts are located in the posterior, the superior, or the anterior compartment of the shoulder and are rarely located in the inferior compartment.3)The symptoms of pain and dysfunction can vary according to the position of the cysts. In this study, we present a case of a paralabral cyst in the inferior compartment of the shoulder in a 79-year-old man whom we treated using arthroscopic decompression. Case ReportThe 79-year-old man admitted to our hospital presented with a chief complaint of left shoulder pain that began and deteriorated without particular trauma from a month before. Specifically, he complained of pain around the posterior compartment of the shoulder, and without particular reason he complained that the pain exacerbated at night. At the time of admittance, the patient scored a visual analogue scale for pain of 6 points. Through physical examination, we found that the range of motion of the left shoulder showed a forward elevation of 160 ; the patient displayed slight restriction in motion. We did not observe other physical or neurological abnormalities that indicated instability. Visually, we could not find evidence for atrophy of the muscles, and muscle strength was within the normal range. Because symptoms prevailed with drug therapy, we carried out plain radiography and MRI. At the preoperative MRI, we found and diagnosed a ganglion cyst, which was fused to the articular surface, with a dimension of 2.5×1.5×2 cm at the inferior labrum, and an inferior labral tear (Fig. 1). Despite conservative treatment of the paralabral cyst through drug therapy, rest, and modified activity for 3 months, the symptoms did not improve; thus, we decided to treat the patient surgically.Under general anesthesia, we placed the patient in the right