One-sided diaphragmatic paralysis is a common phenomenon which is usually a-symptomatic. In case of acute onset or if there is an underlying lung disease, the phenomenon may be symptomatic and even limiting. In this article, we present a patient who arrived with subacute shortness of breath when lying down. She underwent thorough investigations but, as happens in most cases, the cause of the paralysis was not identified and it remains idiopathic. The authors present an overview of the etiology, differential diagnosis and treatment of diaphragmatic paralysis.