BACKGROUND Infant docosahexaenoic acid (DHA) status is supported by the DHA content of breast milk and thus can decrease once complementary feeding begins. Furthermore, it is unclear to what extent endogenous DHA synthesis contributes to status. OBJECTIVE We investigated several determinants, including FADS genotypes on DHA status at 9 mo and 3 y. DESIGN This was a cross-sectional study with Danish infants from 2 prospective studies [Essentielle Fedtsyrer i OvergangskosteN (EFiON) and the Småbørns Kost Og Trivsel (SKOT) cohort] in which we measured red blood cell (RBC) DHA status at 9 mo (n = 409) and 3 y (n = 176) and genotyped 4 FADS tag single nucleotide polymorphisms (SNPs): rs3834458, rs1535, rs174575, and rs174448 (n = 401). Information about breastfeeding was obtained by using questionnaires, and fish intake was assessed by using 7-d precoded food diaries. RESULTS FADS genotype, breastfeeding, and fish intake explained 25% of the variation in infant RBC DHA status [mean ± SD: 6.6 ± 1.9% of fatty acids (FA%)]. Breastfeeding explained most of the variation (∼20%), and still being breastfed at 9 mo was associated with a 0.7 FA% higher DHA compared with no longer being breastfed (P < 0.001). The FADS SNPs rs1535 and rs3834458 were highly correlated (r = 0.98). Homozygous carriers of the minor allele of rs1535 had a DHA increase of 1.8 FA% (P = 0.001) relative to those with the wild-type allele, whereas minor allele carriers of rs174448 and rs174575 had a decrease of 1.1 FA% (P = 0.005) and 2.0 FA% (P = 0.001), respectively. Each 10-g increment in fish intake was associated with an increased DHA status of 0.3 FA%. At 3 y, fish intake was the only significant determinant of DHA status (0.2 FA%/10 g). CONCLUSION Breastfeeding, FADS genotype, and fish intake are important determinants of DHA status in late infancy. The EFiON study was registered at clinicaltrials.gov as NCT 00631046.