ABSTRACT: Myositis ossificans (MO) in the head and neck is a rare heterotropic bone formation within a muscle. Besides fibrodysplasia ossificans progressiva, traumatic and neurogenic forms are described in the literature. We are presenting the case of a 35-year-old female patient with a very rare form of MO of both masseter muscles after 4 weeks of intensive care because of complications (critical illness neuropathy) after chemoradiotherapy. Therefore, special attention should be paid to surgical trauma. As in the present case, radiotherapy, long-time intubation with immobilization and critical myopathy and neuropathy can cause MO with severe problems, such as trismus and reduced mouth hygiene, which can lead to reduced quality of life.