Online self-administered data collection, by reducing the logistic burden and cost, could advantageously replace classical methods based on dietitian's interviews when assessing dietary intake in large epidemiological studies. Studies comparing such new instruments with traditional methods are necessary. Our objective was to compare one NutriNet-Sante web-based self-administered 24 h dietary record with one 24 h recall carried out by a dietitian. Subjects completed the web-based record, which was followed the next day by a dietitian-conducted 24 h recall by telephone (corresponding to the same day and using the same computerised interface for data entry). The subjects were 147 volunteers aged 48-75 years (women 59.2%). The study was conducted in February 2009 in France. Agreement was assessed by intraclass correlation coefficients (ICC) for foods and energy-adjusted Pearson's correlations for nutrients. Agreement between the two methods was high, although it may have been overestimated because the two assessments were consecutive to one another. Among consumers only, the median of ICC for foods was 0.8 in men and 0.7 in women (range 0.5-0.9). The median of energy-adjusted Pearson's correlations for nutrients was 0.8 in both sexes (range 0.6-0.9). The mean Pearson correlation was higher in subjects <= 60 years (P=0.02) and in those who declared being 'experienced/expert' with computers (P=0.0003), but no difference was observed according to educational level (P=0.12). The mean completion time was similar between the two methods (median for both methods: 25 min). The web-based method was preferred by 66.1% of users. Our web-based dietary assessment, permitting considerable logistic simplification and cost savings, may be highly advantageous for large population-based surveys.