Iodine staining and scanning electron microscopy were used to determine the morphological features distinguishing Opisthorchis viverrini from lecithodendriid eggs in human feces. The embryonated eggs of lecithodendriid trematodes differ from O. viverrini by the presence of an iodophilic body, a large mass at the posterior end of miracidium that stains brown in 0.2% iodine solution and the curved miracidium of Phaneropsolus bonnei. All forms of lecithodendriid eggs can be differentiated from those of O. viverrini by a set of morphological features of the shell surface, the knob, the operculum, the shoulder, the shape and size. On the basis of these differences, it is possible to perform differential egg counts.