The similarity of the observed densities of baryons and cold dark matter suggests that they have a common or related origin. This can be understood in the context of the MSSM with right-handed (RH) sneutrinos if cold dark matter is due to a d = 4 flat direction condensate of very weakly coupled RH sneutrino LSPs and the baryon asymmetry is generated by Affleck–Dine leptogenesis along the d = 4 (HuL)2 flat direction. The correct density of RH sneutrino dark matter is obtained if the reheating temperature is in the range 106–108 GeV. A cold dark matter isocurvature perturbation close to present observational bounds is likely in the case of inflation driven by a D-term or by an F-term with suppressed Hubble corrections to the A-terms. An observable baryon isocurvature perturbation is also possible in the case of D-term inflation models.