Increasing multi-ethnicity is likely to make alpha-thalassemia (alpha-thal) more prevalent in Western metropolitan areas. Multiplex polymerase chain reaction (m-PCR) allows rapid and precise identification of most of alpha-thal carriers. With this method, we sought to determine the prevalence of alpha-thal and the corresponding genotype, among all non repetitive consecutive blood samples that had an unexplained microcytosis. These specimens had been sent to the hematology laboratory for a blood count analysis, found to be microcytic, and secondarily tested for ferritin level and hemoglobin (Hb) high performance liquid chromatography (HPLC) profile. Five hundred and sixteen microcytic blood samples were evaluated and 197 samples with normal ferritin and Hb HPLC were studied by m-PCR. Among 196 interpretable PCRs, 48 alpha-thal cases (24.5%) were identified: 28 with a single alpha-globin gene deletion and 20 with two alpha-globin gene deletions. Of these 20 cases, six showed two deletions in cis. None of the erythrocytic parameters studied predicted the presence of alpha-thal deletions. We conclude that a significant proportion (24.5%) of blood counts with microcytosis not explained by an iron deficiency, an inflammatory state or an abnormal Hb on HPLC, are caused by an alpha-globin gene deletion. The pertinence of genetic counseling for alpha-thal based on molecular diagnosis should be evaluated more formally in urban centers where this genetic condition is likely to have an increasing prevalence and clinical relevance.