One of the leading causes of pneumonia in children between 5 to 15 years is Mycoplasma pneumoniae, a bacterium that causes atypical clinical manifestations such as myositis and encephalitis. We report a 5-year-old girl who presented functional limitations of the lower extremities preceded by an upper respiratory infection. Later on, she developed pneumonia and encephalitis. Antibiotics and antivirals were administered due to the clinical deterioration of the patient. IgM serology for Mycoplasma pneumoniae was positive, while the other viral studies were negative. The clinical course was favorable with a progressive decrease in respiratory distress, sensorial disorder, and improvement in the functional limitations of the lower limbs after 15 days of treatment.