BACKGROUND: The recently introduced size 1.5 laryngeal mask airway (LMA) is specifically designed for use in children weighing 5-10 kg. METHODS: We prospectively evaluated its use in 68 patients, mean age 8.7 months, who were undergoing a variety of routine surgical procedures. RESULTS: The overall incidence of complications was high (42%) and was significantly more common in younger patients. Most of these related to poor positioning of the LMA, or airway problems such as obstruction or laryngospasm. Critical incidents occurred in seven patients, and all but one of these was related to the use of an LMA. CONCLUSIONS: The size 1.5 LMA is a useful addition to the range available, although the overall complication rate is considerable and is inversely related to the age of the child.