The capital market equilibrium is derived in a model where asset returns follow a mixed Poisson jump-diffusion process, rather than a simple diffusion process as in the traditional ICAPM. In the resulting JCAPM (CAPM with Jumps) expected returns are still linear in beta, but in addition premia have to be paid for jump risk. When jump risk is diversifiable in the market portfolio the JCAPM reduces to the standard ICAPM, as in Jarrow and Rosenfeld (1984).

Jumps are found to be prevalent in the daily returns of the market indices in the 18 countries investigated, during the time period 1985-89. However, when the year of the crash, 1987, is excluded from the sample, the simple diffusion process gives an adequate description of the market returns in seven countries.