Objective: Several theories of the underlying mechanisms of SIDS have been proposed, one of them is focusing on shock including anaphylaxis. Increased concentrations of mast cell tryptase in post mortem blood have been observed without increased mast cell numbers in lung tissue. The aim was to evaluate the age-related distribution of pulmonary mast cells in infants dying of sudden infant death syndrome and controls. Method: 6 infants (up to 1 year of age) who died of SIDS and 23 controls who died of other non-pulmonary causes were examined. Peribronchial mast cells exhibiting tryptase immunoreactivity were evaluated and quantified in high power fields in lung sections. Results: The number of mast cells in peribronchial regions amounted to 18,9 (± 6,6)/mm2 in children aged 1 month up to 13 months. Mast cells in SIDS cases were 21,2 (± 4,5)/mm2. The difference was not significant (P=0,113, Student'st test). Conclusion: It is unlikely that increased pulmonary mast cells are indicators of SIDS. The role of mast cells in SIDS remains controversial.