During the last two decades, neonatal screening in Europe and North America has expanded substantially. This article examines two recent suggestions for expanding neonatal screening: severe combined immunodeficiency and X-linked adrenoleukodystrophy. With reference to well-established risk-benefit based rationales for screening, it is argued that the case for introducing SCID in neonatal screening is considerably stronger than for introducing X-ALD. For instance, the majority of those screened for X-ALD most likely have a negative risk-benefit ratio of screening: they develop milder symptoms (...) or perhaps no symptoms at all, while still being monitored for a long time. This argument is used as a vehicle for making some general points regarding justified expansions of neonatal screening. First, when considering the expansion of neonatal screening, we should look at a condition specific case-by-case basis. Moreover, future expansions of neonatal screening should stick to the well-established rationales for screening while avoiding risk-benefit slippage. Otherwise, more strict procedures of informed consent are warranted in neonatal screening, procedures that, in the end, risk undermining the benefits of current neonatal screening programmes. (shrink)