Flow visualization observations are described for natural convection flow in rectangular inclined enclosures. Observations are made in air-filled enclosures of small and moderate aspect ratio (0.25 ⩽ Ax ⩽ 7), angles of inclination from 0 to 90 deg and Rayleigh number between 5 × 103 and 2.5 × 105. For the range of parameters considered we determined the transition from stationary to nonstationary flow and the transition from two-dimensional to three-dimensional flow. Also, the different stationary flow structures are described. In addition measurements of the velocity profile of the stationary flow have been performed by means of a laser doppler anemometer. Special attention has been given to the side wall boundary condition of the enclosure.