This paper describes the stability of the stages of change concept of the Transtheoretical Model for three different nutrition behaviors (fat, fruit and vegetable intake) among adult individuals who are unexposed to planned interventions. Secondary analyses were conducted on data collected in control groups (n = 386 and n = 739) of two intervention studies in the Netherlands. Data on dietary intakes and stages of change was collected at baseline and follow up, either 1 year (study 1) or 3 months (study 2) post-baseline. Higher levels of agreement between baseline and follow-up measures of stage of change were found for pre-contemplation and maintenance than for the other stages. However, many forward as well as backward stage transitions occurred between baseline and follow-up also among respondents in pre-contemplation and maintenance at baseline. The results indicate that many stage transitions may occur in individuals, also when they are not exposed to planned interventions. An additional explanation for the stage instability may be low reliability of the staging algorithm. The results imply that if classification into stages of change is used to tailor interventions, these interventions may be tailored to the wrong stage, at least with longer time intervals between stage assessment and intervention. Further research is needed to assess 'spontaneous' stage-transitions in shorter time intervals.