The effect of interparticle forces on Brownian coagulation of aerosols is usually accounted for through a phenomenological sticking probability, i.e., the probability of coagulation upon collision. This probability is customarily assumed to be equal to unity even though it is recognized that it is smaller than unity for very small particles. A Monte Carlo method for the simulation of Brownian coagulation of equal-sized electrically neutral spherical aerosol particles is presented, which takes into account the interparticle forces due to van der Waals attraction and Born repulsion instead of the phenomenological sticking probability. The particle motion is described by the generalized Brownian dynamics. The Brownian coagulation coefficient for particles of unit density, for a Hamaker constant of 10 −12 erg, is calculated over the entire range of Knudsen numbers. For large particles, the results of the simulation agree very well with those provided by the model proposed previously by the authors (1) and also with the Fuchs interpolation formula. In this case the results indicate that the sticking probability is close to unity. For sufficiently small particles, the coagulation coefficient agrees with the lower bound provided by the model proposed by the authors (1). The extrapolation to sufficiently small particles of the model (1) proposed for large particles provides an upper bound with much larger values. For particles of intermediate sizes, the coagulation coefficient is found to be even higher than the values predicted by the model valid for large particles (1). The coagulation coefficients of the particles of intermediary size are greater than those corresponding to a sticking probability of unity whereas those of the sufficiently small particles are much smaller because of the following two opposite effects: (i) As the particle size decreases, the ratio of the decay length of the interaction potential (based on the shortest distance between the particles) and the particle size increases; this relative increase in the range of the van der Waals attraction increases the rate of collisions between particles. (ii) As the particle size decreases, the interaction potential becomes less deep and, as a result, the probability of escape of the particles from the potential well increases. In the intermediary size range, the former effect, which was not accounted for in the model for large particles (being negligible in that case), is more important, whereas for very small particle sizes, the latter effect predominates. The calculated values of the collision efficiency are small for sufficiently small particles, increase with particle size and eventually reach the value of unity for large particles. Extrapolating to particles of molecular dimensions, one can understand why in the cases in which only physical interactions are involved the collision efficiency is negligibly small.