The breast milk concentrations of polybrominated diphenyl ethers (PBDEs; sum of five congeners: BDE-47, -99, -100, -153, and -154) were determined (by GC-ECD) in samples from 93 primiparous women collected from 1996 to 1999 in Uppsala County, Sweden. Dietary and lifestyle factors were also recorded. The mean PBDE concentration was 4.0 ng/g fat and the distribution of samples was skewed with few high values (maximum 28.2 ng/g fat). BDE-47 was the major congener and constituted 59% of the mean concentration of PBDEs. No significant relationship was found between breast milk concentrations of PBDEs and dietary intake of PBDE, age, body mass index, alcohol consumption, or computer usage. After adjustments for these factors, a weak but significant association between PBDE concentrations and smoking was observed. The dietary intake of PBDE for these women was estimated at 27 ng/day, of which fish contributed almost half. After inclusion of 31 additional samples, collected from 2000 to 2001, time trends were studied. The changes in breast milk PBDE levels between 1996 and 2001, similar to the results from another Swedish study on milk from Stockholm mothers, suggest a peak in PBDE concentrations around 1998 and thereafter decreasing levels. However, far-reaching conclusions about PBDE time trends in milk cannot be drawn from this short study.