Parvimonas micra is a rare pathogen for septic arthritis and is known for its subacute onset. We report a case of acute arthritis of the knee caused by P. micra and pseudogout. Initially, calcium pyrophosphate crystals were found in the knee, which were successfully treated with a steroid injection. Only anaerobic cultures became positive. A 16S rRNA PCR-analysis was necessary to identify P. micra as causative agent, a method which is never described before in similar cases. The infection was treated with clindamycin for 6 weeks. This is the third case report of a septic arthritis caused by P. micra and the second which also reports concomitant pseudogout.