In a process for preparing a polyamide based on dicarboxylic acids and diamines in an extruder, a solid mixture comprising a monomer mixture composed of 50 mol % of dicarboxylic acid mixture composed of from 60 to 88 % by weight of terephthalic acid and from 12 to 40% by weight of isophthalic acid, in which up to 20% by weight of the dicarboxylic acid mixture may also be replaced by other dicarboxylic acids, and 50 mol % of hexamethylenediamine which may be up to 20% by weight replaced by other C2-30-diamines, in a corotatory twin-screw extruder for a residence time of from 10 seconds to 30 minutes, is heated to a temperature in the range from 150 to 400° C. while removing steam and if appropriate diamines through venting orifices.