Background: Dermatomyositis (DM) is an autoimmune disease characterized by cutaneous Gottron papules, heliotrope rash, and proximal myopathy. It may also present as a paraneoplastic syndrome that can complicate a variety of different cancers, such as lung, cervical, and breast cancer. However, the association with hepatocellular carcinoma (HCC) is extremely rare. Moreover, to our knowledge, there are no previous reports of colonic perforation following steroid pulse treatment for a DM patient. Case Summary: A 61-year-old male complained of a skin rash that began in his neck and spread to his face and abdomen. On physical examination, the patient was also found to have symmetrical proximal muscle weakness, abdominal pain, heliotrope rash in the periorbital skin, and poikiloderma on his face and abdomen. Serum level of muscle enzymes was remarkably increased. Muscle examination revealed symmetrical proximal weakness. The diagnosis of DM was made, and steroid treatment was started for symptomatic relief. A search for causative malignancy revealed HCC. Despite steroid therapy for DM, his symptoms did not improve. Additionally, C-reactive protein elevation was seen along with severe abdominal pain on day 14 of admission. Shortly after this, the patient died of septic shock due to suppurative peritonitis after perforation of the ascending colon. Conclusion: Here, we present a rare case of DM caused by non-hepatitis-associated advanced HCC with colonic perforation. The cause of colonic perforation is still unclear. This case demonstrates the need to carefully monitor abdominal pain in DM patients as symptoms can be masked by steroid therapy.