Abstract: The invention relates to a process for the preparation of risperidone (chemical name: 3-[2-[4-(6-fluoro-1,2-benzisoxazole-3-yl)-1piperidmyl]ethyl-2-methyl-6,7,8,9-terahydro-4H-pyrido[1,2-a]pyrimidine-4-one) of the formula (I) by reacting 3-(2-chloroethyl)-2-methyl-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-4-one of the formula (II) and 6-fluoro-3-(4-piperidinyl)-1,2-benzisoxazole of the formula (III), in which the reaction is carried out in dry methanol solvent under pressure, at a temperature between 65 and 90° C., the product is recovered by using a methanol/water mixture of specified ratio and if desired is recrystallized from an alcohol.