We report a case of a 42-year-old man who presented with acute epigastric and retrosternal chest pain and exertional dyspnoea, and was subsequently diagnosed with polyserositis secondary to post-Streptococcal mitis infection. A CT scan showed a large pericardial effusion requiring pericardiocentesis, small bilateral pleural effusions and small amount of ascites. Several serological tests were done, which were all found to be normal. Pericardial and pleural fluid aspirates revealed an exudate. Culture of the pleural fluid yielded growth of S.  mitis and this was deemed the cause of the polyserositis, which is rare. The patient made a spontaneous recovery. He was started on colchicine by the cardiologists to help prevent pericardial fluid recurrence and this was continued for 3 months. A dental review confirmed the presence of dental caries, the possible source of infection. On follow-up, the patient remained well with no further relapses.