A healthy 3.5-month-old infant developed septic arthritis with Haemophilus influenzae type f isolated from the knee aspirate and blood. The patient had no obvious risk factors and immunological evaluation revealed no abnormalities. To our knowledge, there are only two reported childhood cases of septic arthritis caused by non-type b H. influenzae, but this is the first one to be reported in a child without an underlying disorder. The importance of serotyping H. influenzae isolates in the H. influenzae type b vaccine era, and the need to look for predisposing factors in paediatric patients with invasive disease caused by non-type b H. influenzae are discussed.