Objective This article reports on the use of focus groups and an experimental participatory activity to investigate factors influencing participants' decisions about what to eat and what to report on food records and food frequency questionnaires.

Design Four focus groups examined participants' experience with diet records and 3 focus groups explored the topic of food portions using a group consensus activity. Twenty-two women participated in the diet record focus groups, and 15 participated in portion estimation groups.

Subjects Focus group participants were equally distributed by age and body mass index values. Each woman completed a 10-day doubly labeled water protocol to measure total energy expenditure, 7 days of diet records (before and during total energy expenditure), and a food frequency questionnaire after the total energy expenditure.

Analysis Transcripts of the focus groups were coded to index categories of responses and to identify themes within and across those responses. Themes discussed in this article are those that were discussed most often and at greatest length by all groups.

Results The diet record focus groups revealed that 2 major factors influenced reporting on diet records: honesty vs social acceptability, and simplifying food intake. The portion estimation focus groups revealed 5 factors that influenced perceptions of portion size: the role of food in the meal, the type of food, personal preferences, product serving sizes, and comparison of personal servings with those of others.

Applications The validity and reliability of self-reported food consumption is greatly influenced by the ways people interpret and respond to dietary assessment instruments. These findings indicate that dietetics professionals need to take extra steps to address issues of accurately recording “bad” foods when training patients to complete diet records. Extra probing is needed when dietary records do not include snacks and include simple meals and a large amount of prepared and packaged food because this may indicate that changes in normal dietary patterns were made in order to more easily complete a dietary record. J Am Diet Assoc. 2000;100:1023–1028.