The present study aimed to evaluate whether there is any association between CYP2D6 alleles and susceptibility to tardive dyskinesia in patients with schizophrenia under treatment. A meta-analysis considered case-control studies determining the distribution of genotypes for any CYP2D6 polymorphism in unrelated tardive dyskinesia cases and controls without tardive dyskinesia among patients with schizophrenia who were treated with antipsychotic agents. Loss of function alleles were grouped together in a single comparison, whereas other alleles (2 and 10) were examined separately. Data were available for eight (n=569 patients), three (n=325 patients) and four (n=556) studies evaluating the effect of the loss of function alleles, the 2 allele and the 10 allele, respectively. Summary odds ratios (ORs) suggested that loss of function alleles increased the risk of tardive dyskinesia significantly [OR=1.43, 95% confidence interval (CI) 1.06-1.93, P=0.021], whereas there was no effect for 2 and inconclusive evidence for 10 (OR=0.82, 95% CI 0.50-1.32, P=0.41 and OR=1.19, 95% CI, 0.89-1.60, P=0.24, respectively). Patients who were homozygotes for loss of function alleles (poor metabolizers) had 1.64-fold greater odds of suffering tardive dyskinesia compared to other patients with schizophrenia, but the effect was not formally significant (95% CI 0.79-3.43). For the risk conferred by loss of function alleles, large studies provided more conservative estimates of a genetic effect than smaller studies (P=0.003). CYP2D6 loss of function alleles may predispose to tardive dyskinesia in patients with schizophrenia under treatment, but bias cannot be excluded.