The aim of this study was to evaluate the use of the DietAdvice website, a self-administered online dietary assessment, in the context of a dietary intervention randomized controlled trial [ACTRN 12608000425392]. Data available from a total of n=118 volunteers recruited to the dietary trial and using the website in the clinic at t=0, 3 and 12mo was compared with that obtained from diet histories (DH) and 3-day food record (FR). Fasting blood samples from these time points were also correlated with the macronutrient values obtained. Complete web based records were obtained for 65% of participants at t=0, 83% at t=3 and 75% at t=12mo. At baseline, values for dietary energy (p=0.01), carbohydrate (p=0.036), saturated (p=0.001) and monounsaturated (p=0.014) fat were significantly different for all assessment methods while at 3 months only that for energy (p=0.041) was significantly different. Overall stronger correlations between the macronutrient values from DietAdvice and blood biomarkers were observed at t=12months. In both settings, the data from DietAdvice was most similar to that of the 3-d FR . It appears that trial participants had difficulty using DietAdvice website independently. Compared with data obtained from the primary healthcare setting the limited assistance with the website provided to trial participants may have affected the results.