<span name="style_bold">Aim:</span> To describe the cases of delusional parasitosis observed in the Laboratory of Medical Entomology, School of Microbiology, University of Costa Rica during 2001-2011.   <span name="style_bold">Methods:</span> Nine cases compatible with delusional parasitosis are described. The “diagnostic evidence” provided by patients as cause of their illness is also analyzed.   <span name="style_bold">Results:</span> These patients referred chronic problems on skin and scalp with signs and symptoms attributed, in their opinion, to different types of arthropods. These patients had already been evaluated by a physician and had been unsuccessful with the expected diagnosis. The samples provided included several types of arthropods, such as, psychodinae (Diptera: <span name="style_italic">Psychodinae</span>), booklice (Psocoptera), true bugs (Homoptera), flies (Diptera: Cyclorrhapha), ants (Hymenoptera: Formicidae), Isoptera and house spiders (Arachnida: Aranea), that are irrelevant in terms of medical importance. Other materials such as grains, vegetable fibers, fibrin clots, and pieces of skin were also detected.   <span name="style_bold">Discussion:</span> We emphasize the importance of a correct diagnosis and identification of possible causes of this syndrome before administering treatment with anti-parasitic drugs We emphasize the importance of a correct diagnosis and identification of possible causes of this syndrome before administering treatment with anti-parasitic drugs

Affective disorders; psychotic; parasite; insect; diagnosis