We demonstrate, for the first time, the direct writing of curved optical waveguides in monocrystalline silicon with curve radii from 2 mm to 6 cm. The bending loss of the curved waveguides is measured and a good agreement with theoretical values is found. Raman spectroscopy measurements suggest the formation of inhomogeneous amorphous and polycrystalline phases in the laser-modified region. This direct laser-writing method may advance fabrication capabilities for integrated 3D silicon photonic devices.