Barth syndrome (BTHS) is an X‐linked autosomal recessive disorder characterized by neutropenia, cardiomyopathy and growth retardation. BTHS was first described as mitochondrial disease affecting neutrophils as well as cardiac and skeletal muscles. Patients with neutropenia may have extremely low levels of circulating neutrophils and suffer from recurring sometimes life‐threatening bacterial infections. Sepsis is not infrequent, may occur unexpectedly in a patient with no history for pronounced bacterial infections and may lead to death. The reduced level of circulating neutrophils suggests either a reduced production of myeloid cells in the bone marrow and premature apoptosis or aberrant clearance of neutrophils in peripheral blood. The underlying molecular defects are truncation, deletion or substitution mutations in the TAZ gene that appear to result in loss‐of‐function of the gene product tafazzin. Molecular mechanisms triggering neutropenia and cardiomyopathy in BTHS remain largely unclear. The current review focusses on recent advances in the understanding of molecular and cellular bases of neutropenia in Barth syndrome and covers the functional implications of the TAZ mutations, experimental models for neutropenia, the specific cellular abnormalities triggered by loss of TAZ function and potential novel therapeutic strategies for restoring the normal phenotype.