Planning, environmental conditions and their impact of 104 small scale enterprises were studied within a longitudinal design. There was a positive relationship between detailedness of planning and success in the first wave. In both waves environmental hostility and uncertainty (i.e. an unfavorable environment) moderated the relationship between planning and success. There was no direct long-term effect of planning on success. However, there were significant contempaneous moderator effects with high planning being particularly important for having success in unfavorable environments. Thus, this study supports a contingency view on the relationsship between planning and sucess.