This study aimed to evaluate the validity and reproducibility of a semi-quantitative food frequency questionnaire (FFQ) to estimate nutrient intake among Portuguese pregnant women. A sample of 101 pregnant women completed a 3-day food diary (FD) in each pregnancy trimester (reference method) and an interviewer-administered FFQ in the immediate post-partum period. Ranking women according to their usual intake showed that, on average, 65% were classified into the same +/-1 quintile and 2.4% into opposite quintiles by the two methods. Energy-adjusted and de-attenuated correlation coefficients ranged from 0.20 (protein) to 0.58 (riboflavin). Similar results were obtained when the FFQ was compared to each trimester-specific FD. To assess the FFQ reproducibility, 70 women in their third pregnancy trimester were interviewed twice within a 2-week interval. The level of agreement was high, with > or = 75% of the participants being classified into the same +/-1 quintile by the two administrations for 13 of the 15 nutrients examined. A review of the published literature revealed that this is the first FFQ to take the whole pregnancy as its reference time window. Our findings showed that a single administration of this FFQ in the immediate post-partum period is a valid tool to rank Portuguese pregnant women according to their intakes.