Obesity hypoventilation syndrome (OHS) is a condition in which an individual with a body mass index >30 kg/m2 develops daytime alveolar hypoventilation (defined as a resting PaCO2 >45 mmHg) that cannot be attributed to other pathologies. It is a condition with increasing prevalence and rising cost to healthcare systems worldwide. Right heart failure and pulmonary hypertension are well-known complications of this syndrome. Here, we present the case of a female patient with OHS who presented to our centre with severe pulmonary hypertension, which resolved with appropriate treatment. We also review this clinical condition and its diagnosis and management.