Approximately 90% of skin infections are thought to be attributable to Staphylococcus aureus and Streptococcus pyogenes, along with some anaerobic bacteria such as Bacteroides and Prevotella species, which are considered significant causative agents in post-operative skin infections especially in diabetics. Species from the anaerobic Porphyromonas genus are known to cause oral infections, but rarely cause infection of the skin. In this case report, we describe a subcutaneous abscess caused by Porphyromonas gingivalis in a 67-year-old man who had started chemotherapy for lung cancer (cT3N3M0 stage Ⅲ B) three days prior to consulting a dermatologist. On clinical examination, a fist-sized mass with a hot sensation was observed in the left temporal region of the face, and treatment with cefazolin was commenced at 6 g/day. After three days, the mass was drained via skin incision and pus culture was performed, which revealed infection with P. gingivalis. The patient was successfully treated with abscess drainage and antibiotics therapy. We suggest that in tandem with immunosuppression, P. gingivalis could be a cause of skin infections.