The kinetics of diamond nucleation on solid substrate surfaces can be derived from the particle size distributions observed by scanning electron microscopy, when the single-particle growth law is known, and the deposition time period is such that the particles are still well separated. The ''observed'' nucleation behaviour suggests two main features. (1) The nucleation occurs on certain sites, whose number is limited. (2) The nucleation shows a temperature-dependent incubation time. To justify these trends a nucleation kinetic model is formulated, which relates the incubation time to the time required to form a critical diamond cluster on each nucleation site. In our model the existence of a critical cluster and of an incubation time is related to the misfit strain generated at the diamond-substrate interface.