An accurate model has been developed to study photonic crystal fiber Raman amplifiers. The proposed approach calculates the Raman gain efficiency starting from the knowledge of the fiber cross-sectional characteristics, i.e., the geometric parameters and the germania concentration in the doped area. The model allows the study of the Raman amplification process in a photonic crystal fiber with any air-hole dimension and disposition, with or without a central doped area, as well as in standard single-mode fibers with an arbitrary refractive-index profile. This flexibility allows identification of the optimum values of the physical and geometrical photonic crystal fiber parameters, and thus it guarantees an efficient design for Raman amplifiers. For example, a Raman gain of 13.7 dB at 1554.8 nm has been obtained with a 6-km-long low-loss germania-doped triangular photonic crystal fiber with d/Λ = 0.44 and Λ = 4.2 μm.