AbstractMethylmalonic acidemia (MMA) is an autosomal recessive disorder that can be classified into two types: (1) vitamin B12‐responsive and (2) vitamin B12‐non‐responsive. In MMA cases with long‐term survival, renal failure is often a problem, and timing for kidney transplantation for MMA is controversial. We encountered a vitamin B12‐non‐responsive MMA case for which regular hemodialysis for renal failure was initiated; the patient was 16 years old when she first received regular hemodialysis and 35 years old when she developed pulmonary artery hypertension (PAH). PAH can complicate regular hemodialysis; however, PAH in this case was considered to be a complication of MMA because it was responsive to medical treatment and reversible. In this report, we discuss the role of regular hemodialysis in MMA and the causal relationship between MMA and regular hemodialysis for PAH.