Irritable bowel syndrome (IBS) is one of a broad category of disorders called functional gastrointestinal disorders that manifest with abdominal pain and diarrhea or constipation without a known organic cause. Post-infectious IBS (PI-IBS) refers to the development of IBS following gastrointestinal infections. Various parasites, including Blastocystis spp. have been implicated as potential causes of PI-IBS. Blastocystis spp. is a unicellular parasite colonizing the gastrointestinal tract of humans and many animals. Several factors such as subtype, parasite load, and host-related factors may influence the outcome of Blastocystis infection. Several studies have indicated a correlation between the presence of Blastocystis spp. and IBS as it is frequently found in patients with IBS. While some studies have suggested a link between the presence Blastocystis ST-1 and ST-3 with IBS, most have failed to associate certain subtypes with the development of IBS. Inflammation, dysbiosis, and disruption of gut homeostasis are the major suggested mechanisms by which Blastocystis spp. may cause IBS.