The present study explored the histopathological impacts of the pyrethroid pesticide cypermethrin on gills and trunk mesonephroi of guppy fish (45-day-old) juveniles. Five-day-old guppy larvae were exposed to 7x10-4 or 9.3x10-4 μ M/L of cypermethrin only once for 48-hours. Afterward, they were left to grow (in cypermethrin-free aquaria) until they reach 45-days-old. The juveniles were removed from the aquaria, anesthetized, dissected out and their gills and mesonephroi were processed for paraffin embedding, stained with haematoxylin and eosin, examined by light microscopy, photographed and described. The severity of the observed histopathological changes in gills and mesonephroi of cypermethrin-exposed juvenile's were concentration-dependent. In gills, the lesions were represented by hyperplasia of primary lamellae, shortening, fusion, epithelial lifting of the secondary lamellae; stasis; twisting of the primary lamella; leukocytes infiltration; rupture of the lamellar epithelium; focal proliferation of primary and secondary lamellar epithelial cells; hemorrhages; telangiectasia; hyperactivity of mucous cells and necrosis. In kidneys the histopathological changes included: glomerular damage, dilated capsular space, collapse of glomerular tuft, fluid accumulation and enlarged Bowman's space, dilatation of renal tubules, atrophy and pyknosis of renal epithelium, necrosis and excessive proliferation of the hematopoietic tissue.