The influence of leaf area on tomato yield was evaluated, both by simulations and experimental work. Simulated crop growth results from daily crop gross assimilation rate minus maintenance respiration rate, multiplied by a conversion efficiency factor. Dry matter partitioning is simulated based on the relative sink strengths of the plant organs. Within the plant, individual fruit trusses and vegetative units are distinguished. Leaf area increase is calculated based on temperature, unless a maximum specific leaf area is reached. In the standard situation leaves from a vegetative unit are removed one week before the truss above this unit is harvest ripe. Leaf removal could also be based on maintaining a desired leaf area index (LAI). Measurements at 7 farms showed that in the summer season light interception was on average 90%, with values varying between 86% and 96%. Three different LAI treatments were tested by picking different numbers of old leaves. Reference, high and maximum LAI resulted in average LAI of 3.3, 3.6 and 4.1 m2 m-2, respectively, and equal yields of 66 kg m-2. The model predicted a yield increase of 1.5% for the maximum LAI treatment compared to the reference, with LAI being input to the model. Simulated yield when leaf picking was based upon a desired LAI of 4, was 4% higher than for a desired LAI of 3, with hardly any effect at higher LAI. Simulations showed that removal of young leaves favored partitioning to the fruits but decreased LAI and total yield. However, if removal of old leaves was delayed such that an LAI of 3 m2 m-2 was maintained, removal of every second young leaf improved yield by 10%. Methods of optimizing yield by controlling LAI are discussed