  We use structural information from diffusion Monte Carlo calculations for
two--dimensional 3He to calculate the effective mass. Static effective
interactions are constructed from the density-- and spin structure functions
using sumrules. We find that both spin-- and density-- fluctuations contribute
about equally to the effective mass. Our results show, in agreement with recent
experiments, a flattening of the single--particle self--energy with increasing
density, which eventually leads to a divergent effective mass.
