The nutritional sins of the mother… Prenatal exposures of a mother can affect the health of her offspring, but how? Radford et al. found that the male progeny of undernourished pregnant mice had altered DNA chemistry in their sperm. In addition, the offspring displayed compromised metabolic health. The specific affected genes not only lost DNA methylation but also lacked the normal sperm DNA packaging factors (protamines) and instead were enriched in nucleosomes. Thus, when subjected to a suboptimal prenatal environment, offspring feel the effects of the maternal assault. Science , this issue p. 10.1126/science.1255903 Prenatal assaults change DNA methylation and chromatin structure in sperm and affect offspring. Also see Perspective by Susiarjo and Bartolomei Adverse prenatal environments can promote metabolic disease in offspring and subsequent generations. Animal models and epidemiological data implicate epigenetic inheritance, but the mechanisms remain unknown. In an intergenerational developmental programming model affecting F 2 mouse metabolism, we demonstrate that the in utero nutritional environment of F 1 embryos alters the germline DNA methylome of F 1 adult males in a locus-specific manner. Differentially methylated regions are hypomethylated and enriched in nucleosome-retaining regions. A substantial fraction is resistant to early embryo methylation reprogramming, which may have an impact on F 2 development. Differential methylation is not maintained in F 2 tissues, yet locus-specific expression is perturbed. Thus, in utero nutritional exposures during critical windows of germ cell development can impact the male germline methylome, associated with metabolic disease in offspring.