Abstract: A highly-pure cyanuric acid is manufactured in a continuous process whereby urea and/or biuret are dissolved in an inert solvent and circulated at a high velocity and a temperature in the range of about 180.degree. C. to about 250.degree. C. through a loop between a heat exchanger and a forced circulation evaporative crystallizer body. Cyanuric acid crystallizes from the reaction mixture as it circulates to form a slurry. Ammonia formed during the reaction is removed at reduced pressure as the reaction mixture enters the evaporative crystallizer body. A portion of the slurry of cyanuric acid is continuously removed as it circulates through the loop and may be filtered to recover the cyanuric acid. The filtrate is returned to a feed tank and additional solvent, urea or biuret added to meet the concentration desired in the reaction mixture. The solution from the feed tank is added to the reaction mixture circulating through the loop at a rate to replace the volume of cyanuric acid slurry that is removed.