Mycoplasma hominis (M. hominis) frequently colonizes the genital tract, but is rarely isolated from the respiratory tract. Dissemination of M. hominis has been documented in women with a febrile illness after delivery. Spontaneous recovery is the rule. A 32-year-old woman in the 29th week of pregnancy was hospitalized for pneumonia. She had to be ventilated for respiratory insufficiency and thoracic empyema. The child was delivered by section due to signs of stress in cardiotocography. In the ensuing days the mother's condition worsened, with fever, weight loss and persistent pleural effusion. Even after decortication and treatment with ceftriaxone fever and pleural effusion persisted. M. hominis was found in pleural fluid cultures. Treatment with doxycycline led to rapid defervescence and an improvement of the patient's condition.