The pyomyositis is still being a rare disease in our environment. A review of this illness is made as a result of a new case, which shows some peculiarities that differ it from others published previously: the patient showed a basic medullary carcynoma of thyroid with cerebral metastasis and the responsible germ was a Streptococcus pneumoniae. The immunodepressor factors which are presented at most patients who suffer a pyomyositis, the clinic picture so suggestive and the image methods we dispose nowadays, should serve to suspect its diagnostic in an earlier way, proceeding to its bacteriological confirmation before illness evolves to stages as advanced as in the shown case.