The relationship between Registered Dietitians’ (RDs) knowledge, attitude and behavior in relation to Very Low Calorie Diets (VLCDs) was investigated. Ninety-nine Rds from Oregon and Washington completed a questionnaire about VLCDs. Knowledge, attitude and behavior scores were correlated to determine relationships between the three parameters. The results showed that as the subject's knowledge score increased, their attitude score also increased (r=0.8, p< 0.01), indicating as the knowledge about VLCDs increased, their opinion of VLCD safety and effectiveness also increased. There was also a correlation between the attitude scores and the behavior scores (r = 0.7, p < 0.01). The dietitians were more likely to promote or be involved in a BLCD if they had a positive attitude about their effectiveness. The participants’ knowledge scores were also correlated with their behavior score (r = 0.7, p < 0.01), suggesting that knowledge about VLCDs increased the participant's likelihood of using or referring someone to a VLCD. This study suggests that Rds tend to use or refer clients to VLCD's when they possess knowledge about VLCDs and have a positive attitude about their effectiveness.