Parallel plate models are inadequate to describe the hydraulic and transport properties of natural fractures with rough surfaces. A two-dimensional numerical simulation of flow and solute migration in a fracture with fractal surfaces is presented. The macroscopic transport properties of the fractures are derived by comparison of the numerical simulations to predictions of a one-dimensional advection dispersion model. This makes it possible to determine effective dispersivities and solute velocities for the mathematically generated surfaces. The effects of adsorption, travel distance and channeling phenomena on the transport properties are examined. The modeling indicates that the effective velocity of the solute differs from that of the average fluid particle due to transverse and longitudinal dispersion and diffusion. These conclusions agree with field measurements of flow and transport in fractures. ¿1991 American Geophysical Union