A fatal pulmonary air embolism, confirmed by an oriented necropsy, is described in a 25-day-old premature and small-for-gestational-age neonate. The embolism was suspected after air bubbles were detected in the infusion line. The air bubbles originated from a male Luer-lock to male Luer-lock connector, which was part of a specific assembly of the perfusion line. A solution to this problem is thereby proposed. We recommend caution in using complex infusion line assemblies because such complications are probably underestimated.