A refined leaf growth submodel was incorporated in an existing wheat crop growth model. The submodel calculated daily green leaf area expansion per plant by taking into account plant population, crop age, interplant competition, temperature and crop water status. After calibration, the submodel was tested against independent data. Statistical comparisons between simulated and observed green leaf area index through several growing seasons yielded an index of agreement of 0.88. The mean absolute difference between simulated and observed maximum green leaf area index was 21% of mean observed values. The submodel performed satisfactorily over a wide range of weather conditions, plant populations and cultivars.