Euthanasia is performed on occasion, even on newborns, but is highly controversial, and it is prohibited by law and condemned by medical ethics in most countries. To characterise and compare the judgments of lay persons, nurses, and physicians of the acceptability of actively ending the life of a damaged newborn. Convenience samples of 237 lay persons, 214 nurses, and 76 physicians in the south of France rated the acceptability on a scale of 0-10 of giving a lethal injection in 54 scenarios composed of all combinations of 4 within-subject factors: gestational age of 6, 7, or 9 months; 3 levels of severity of either perinatal asphyxia or of genetic disease; attitude of the parents about prolonging care unknown, favourable, or unfavourable; and decision made individually by the physician or collectively by the medical team. Overall ratings were subjected to cluster analysis and each cluster to analysis of variance and graphic representation. Lay persons (mean acceptability rating 4.29) were significantly more favourable to euthanasia than nurses (2.84), p < .005, or physicians (2.12), p < .005. Five clusters were found with different judgment rules, i.e., how the information was integrated. More physicians (30 per cent) than nurses (14 per cent), p < .01, or lay persons (11 per cent), p < .01, rated euthanasia as never, under any condition, acceptable. Most, however, asserted that it was increasingly acceptable as the factors combined to favour it, especially when the parents desired to stop treatment. More physicians (45 per cent) and nurses (46 per cent) than lay persons (21 per cent), p < .01, used a complex conjunctive rule (level of parent's attitude x level of severity of damage x consultation with team or not) rather than a simple additive rule. Unlike law and medical ethics, most of the lay persons, nurses, and physicians judged the acceptability of euthanasia as a function of the circumstances. Most health professionals combined the factors in a conjunctive (multiplicative), rather than additive, fashion in accordance with legislation for adults in The Netherlands and elsewhere that requires a set of criteria to be fulfilled before it is legitimate to end a patient's life.