We present experimental results on the light transmission and intermode power exchange in multimode fibers with rough surfaces. The experiments were performed with chemically etched 200-m-diameter cores of fused silica fibers that can support up to 700ϫ 700 guided modes at the wavelength employed, Ϸ 0.6 m. After propagation through some rough fiber section the mode power profile acquires a Gaussian shape that propagates along the mean axis of the corrugated fiber, with a slowly reducing radius ͑ϰ1/ ͱ z͒, and practically without attenuation of the central intensity. These features, and other observed characteristics, are reproduced with a theory that assumes a ballistic regime of light propagation through a one-dimensional slab waveguide, relating the characteristic propagation lengths to parameters of the fiber surface roughness.