BACKGROUND Mondor's disease (MD), or sclerosing superficial thrombophlebitis of the veins of the anterior thoracic wall, is a rare condition of unknown cause that usually involves the superior epigastric vein, producing a visible and palpable Mondor cord. This report describes a 27-year-old Japanese woman presenting with left chest wall pain due to palpable and visible sclerosing superficial thrombophlebitis. CASE REPORT We present the case of a 27-year-old Japanese woman who presented with 8 days of left chest wall and upper abdominal pain. Physical examination revealed a firm, palpable cord in the painful area. Chest wall ultrasound revealed a tubular and anechoic superficial cord. Doppler imaging demonstrated normal blood flow surrounding the cord, with no blood flow within. Computed tomography (CT) revealed a subtle structure beneath the lower left breast skin and without breast or lung involvement. We diagnosed her as having MD, and she was treated with non-steroidal anti-inflammatory drugs (NSAIDs). Her pain gradually improved in 3 weeks and the cord disappeared after approximately 2 months. CONCLUSIONS Mondor's disease can be distressing and painful for patients. Clinicians should be aware of this rare and benign disease when a longitudinal painful cord is found in the torso wall. Pain relief and reassurance are typically adequate until resolution. In addition to ultrasonography, CT is also important for diagnosing MD. This report of a rare diagnosis of MD highlights the importance of accurate and timely diagnosis and investigating the patient to exclude superficial and deep venous thrombotic disease.