AgInSe2 is a member of the ternary semiconductor I-III-VI2 family With chalcopyrite structure. The experimental knowledge of the defect mechanisms in this compound is scarce or nearly non-existent. The purpose of this paper is to identify the type of vacancies and to determine the activation energies of their levels making use of both Hall and photoluminescence measurements (PL). Positron lifetime measurements have been used to investigate the active vacancies in AgInSe2 caused by deviations from ideal stoichiometry. Two donor levels at 27 meV and 80 meV have been detected, which are assigned to V-Se and In-Ag, respectively. The positron bulk lifetime was estimated to 284 +/-2 ps.