Background Extrapulmonary manifestations of Mycoplasma pneumoniae infection are uncommon and include hematologic, gastrointestinal, musculoskeletal, dermatologic, and neurologic complications. Neutropenia on the other hand can be caused by a variety of causes including infections. The microorganisms that are commonly associated with neutropenia are: viruses (Epstein-Barr virus, Cytomegalovirus, hepatitis viruses, human immunodeficiency virus, parvovirus B19, influenza, measles), bacteria (Salmonella, Brucella, Bordetella pertussis, Rickettsia), mycobacteria and rarely fungi (disseminated histoplasmosis). Aims Based on the observation that some of our patients that were evaluated for neutropenia had serologic evidence of recent Mycoplasma infection we hypothesised that Mycoplasma pneumoniae might also be a cause of neutropenia in children. Methods To this aim we retrospectively studied the medical records of all patients that had been hospitalized in a tertiary pediatric department during a 17-month period because of a serologically proven Mycoplasma pneumonia infection (positive IgM antibody titers). The demographic characteristics (age, gender), the clinical presentation, medications and other laboratory parameters were also recorded. Neutropenia was defined as an absolute neutrophil count below the 3rd percentile for age and gender. Every patient was matched for age and gender with another patient with similar clinical presentation but in whom antibodies against Mycoplasma pneumoniae were not detected. Student's t-test and chi-square test were used for statistical analyses as appropriate. Results In total 290 patient were tested for Mycoplasma. Ninety patients (50 females) with positive IgM antibodies againt Mycoplasma pneumoniae were identified. Amongst them 18 patients (20%) were also found to have neutropenia (four severe, four moderate, and 10 with mild neutropenia). Mean age (±SD) was 7.11 (±3.67) years. Mean neutrophil count was 1045/mm3. Thirteen patients (72%) presented with a respiratory tract infection, two were investigated because of fever of unknown origin, one for ITP, one for parotitis and one for cervical lymphadenopathy. All patients recovered from their neutropenia. This group was then compared with the patients that had negative antobodies for Mycoplasma, in which 7 cases of neutropenia were recorded (7.8%). Comparison with chi-square test based on a two by two table showed that this difference is statistically significant (p<0.05). Conclusion Infection with Mycoplasma pneumoniae is usually associated with hemolytic anemia. There are only a few reports of other hematologic toxicities in humans. In this study we showed that Mycoplasma infection might be associated with a form of a transient post-infectious neutropenia in 20% of the study group. Given the fact that evaluation for neutropenia maybe time consuming and expensive, it is important for practitioners to be aware of this rare complication of Mycoplasma infection. Moreover, should this observation be confirmed, the administration of an appropriate antibiotic might be beneficial and shorten the duration of the neutropenia.