A method and device for producing crystalline active ingredient particles. The active ingredient is crystallized from a supersaturated solution on the surface of particles of the active ingredient. A suspension of active ingredient particles is subjected to wet grinding in a supersaturated solution of the active ingredient in a first module. At least a part of the suspension is fed from the first module into the second module where it is cooled and simultaneously subjected to ultrasound. The suspension is fed back into the first module after cooling and being subjected to ultrasound. Active ingredient solution and optionally antisolvent are added to the suspension and active ingredient particles and liquid phase are extracted. A relative supersaturation of the active ingredient in the liquid phase of the suspension, relative to the entire liquid phase, is &nlE90%, and the extracted active ingredient particles comprise a mean particle size of 10-500 &mum.
