In accordance with the global trend and in the Netherlands approximately 45% of the population is overweight. Existing studies show that patient self-management can reduce these figures and but medical non-adherence is a persistent problem. eHealth can potentially increase adherence to self-management. Consequently and we designed a persuasive computer assistant and evaluated its influence on self-management and i.e. and the use of an online lifestyle diary called DieetInzicht.nl. The assistant is represented by an animated iCat and which shows different facial expressions and provides cooperative feedback following principles from the motivational interviewing method. We conducted a randomized controlled trial with 118 overweight people over a period of four weeks and studied the difference between diary use with and without computer assistant feedback. Results show that the computer assistant contributed to filling in the diary more frequently and reduced the decline in motivation to perform self-management and lowered the (reported) BMI and and improved the ease of use. Furthermore and diary use increased knowledge of maintaining a healthy lifestyle. Finally and personal characteristics and i.e. and locus of control and vocabulary and computer experience and age and gender and education level and initial BMI and explained the variance in the diary use and its outcome. Of the 118 participants 35 filled in the closing survey and covering motivation and BMI and lifestyle knowledge and ease of use and which implies that the findings based on these results are mainly representative for motivated participants. In general and this study shows that the Dieetinzicht eHealth service and including a personal computer assistant and is likely to support motivated overweight people and lifestyle related diseases to get a better insight in and adhere to their self-management