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Infections with the lung fluke, Paragonimus kellicotti,have been diagnosed in a variety of domestic and wild animals and humans in USA and Canada. Although there are many species of Paragonimusin other parts of the world; P. kellicottiis the only species definitively diagnosed in USA and Canada. Fresh water snails (several species) and crayfish (mainly Orconectesspp.) are its intermediate hosts. Humans and animals become infected with P. kellicottionly by ingesting metacercariae encysted in the heart of crayfish. After ingestion, the fluke penetrates intestinal wall, enters peritoneal cavity, and reaches pleural cavity by direct penetration of diaphragm, 2–3 weeks post inoculation (p.i.). Young flukes penetrate lungs and become encysted in pulmonary tissue, often in pairs. Time to maturity is around 4–7 weeks p.i. Eggs are coughed up, swallowed, and are excreted in feces. Although the parasite has been known for more than a century, there has been an upsurge of human infections in the USA. Here, I review P. kellicottiinfections in naturally infected hosts. Pathogenesis, diagnosis, and treatment in parasite-free cats and dogs experimentally infected P. kellicottiare reviewed to shed light on the pathogenesis of human paragonimiasis. Problems and challenges facing diagnosis of paragonimiasis, especially non-pulmonary infections, are discussed. Fluke stages are deposited in Smithsonian Museum.