Scale effects on cavitation are defined here as departures from the classical similarity relations when changing size, velocity, and/or properties of the fluid. The various phenomena governing such scale effects are examined and the resulting similarity laws, together with some expected scale effects, are tabulated. The theoretical expectations are then compared with extensive test data on desinent cavitation in cold water. This comparison leads to two different sets of plausible relationships for cavitation attached to a streamlined body, and cavitation not attached to a solid wall. However, the conclusions drawn are only tentative and qualitative, clearly indicating the need of further careful experimentation and analysis.