Single crystals of Csl, CsI:TI, and CsI:TI, Bi were grown by the vertical Bridgman method. We studied the effect of Bi 3+ codoping on the CsI:TI X-ray-induced afterglow. Thermally stimulated luminescence measurements were carried out in order to investigate the role of traps. The results showed a remarkable reduction of afterglow, of about an order of magnitude, and of trap concentration by Bi codoping. These improvements could be related to a possible role of Bi in the compensation of intrinsic nonstoichiometry defects.