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We report the observation of correlated photon pairs generated by spontaneous parametric downconversion of a 400-nm pump pulse in a quasi-phase-matched KTiOPO_4 nonlinear waveguide. The highest ratio of coincidence to single-photon count rates observed near 800??nm exceeds 18%. This suggests that nonlinear waveguides will be a promising source of correlated photons for metrology and quantum information processing applications. We also discuss possibilities of controlling the spatial characteristics of the downconverted photons produced in multimode waveguide structures.