A national training project in the diagnosis of intestinal parasites was conducted in 1997. An initial national course was followed respectively by courses in the Central, Eastern, and Western Provinces. Our results showed that Cryptosporidium parvum, Cyclospora cayetanensis, and leukocytes showed a significantly lower percentage of errors after the training than before (p < 0.01). The same occurred with Entamoeba histolytica/E. dispar and Chilomastix mesnilii (p < 0.05). Among the helminths, Taenia spp., Fasciola hepatica, and hookworm showed significantly fewer errors after the training (p < 0.01). In the other specimens, few mistakes were found both at the beginning and after the training, and the percentage of errors did not change (p > 0.05). Furthermore, when comparing scores before and after training, a significant increase in median scores appeared in the Central Provinces (p < 0.05), Western Provinces (p < 0.01), and in the entire series (p < 0.01). The results showed the effectiveness of this intervention; these periodic mandatory training courses should be developed together with national programs for quality assessment in Parasitology.