In this paper we report on the development of a microsimulation model of daily activity patterns in the context of a regional planning model. One of the aims of the simulation model is to predict traffic flows on a transportation network for various times of the day by using available statistical data sources as input. We first discuss the general conceptual underpinnings of the model, and against a brief discussion of existing activity-based models of transport demand we outline the major differences between these models and the current one. Next, major operational decisions, data input, and model architecture are discussed, followed by an illustration of the model for the Eindhoven region in the Netherlands. We conclude the paper by critically discussing its basic assumptions and identifying avenues of future research.