Rett syndrome is a progressive pervasive neurodevelopmental disorder that affects female patients and is the second most common cause of intellectual disabilities in the female gender, with an incidence of 1:10,000 to 1:15,000 live born girls. The classic form of Rett syndrome in 95% of cases is caused by de novo mutation on the X-chromosome-linked gene encoding the methyl-CpG-binding protein 2. It is characterised by developmental delay/ intellectual disabilities, ataxia, epilepsy, characteristic stereotyped movements of the hands and loss of their normal function, and breathing disorders. There is no effective cure, but early recognition of the disease and early treatment, primarily antiepileptic and respiratory, can delay the onset of further complications. Breathing disorders including apnoea, hyperventilation, rapid and shallow breathing, breath-holding and spontaneous Valsalva manoeuvres result from ventilatory perfusion inequality, and are the result of a number of factors, including oxidative stress and chronic subclinical inflammation. The aim of this case report is to present a girl with Rett syndrome who was treated with antibiotics on several occasions for radiologically persistent changes in the right upper pulmonary lobe, as the changes were understood as pneumonic infiltrate. Changes of the upper right pulmonary lobe on computed tomography of the thorax are found in 50% of children with Rett syndrome, are chronic in nature and do not require antibiotic treatment. Therefore, caution should be exercised when interpreting radiological recordings so that antibiotic therapy is not unnecessarily prescribed.