Radiofrequency ablation is one of the most commonly used therapies for potentially curative small hepatocellular carcinoma. Although radiofrequency is usually a safe procedure, severe and potentially fatal complications can happen. This is a case of a 72 years old woman with cirrhosis secondary to Metabolic Associated Fatty Liver Disease (MAFLD), who presented recurrent hydrothorax after treating hepatocellular carcinoma (HCC) with radiofrequency ablation (RFA), and in which diaphragmatic perforation was subsequently diagnosed. We reviewed the differential diagnosis and management in a pleural effusion after a radiofrequency procedure. Although diaphragmatic perforation is an uncommon complication after RFA procedure, this case aims to help clinicians being aware of non-habitual complications.