In a retrospective study covering a 13-year period and a population of 817,900 inhabitants, 13 cases of invasive infection caused by Haemophilus species other than Haemophilus influenzae were found. Ten of the infectious episodes were caused by Haemophilus parainfluenzae and three by Haemophilus aphrophilus. The clinical manifestations comprised endocarditis, meningitis, pleuropneumonia, epiglottitis and septicaemia from an unknown focus. These 13 infectious episodes caused by uncommon Haemophilus species constituted less than 3% of the total number (473) of invasive Haemophilus infections registered during the same period of time. Invasive H. influenzae infections were more common in all age groups than infections caused by other Haemophilus species. In contrast to H. influenzae infections, which predominate in childhood, invasive infections due to uncommon Haemophilus species had no predilection for any age group.