The soybean cyst nematode, Heterodera glycines, is a common pest of soybean in Wisconsin and the U.S. The SCN is undetected in many fields and may be one of the most widespread diseases affecting soybean. Yield losses of up to 30% can occur with no apparent symptoms on soybean stand or plant vigor. Population densities build slowly over time, usually in a very patchy pattern. Declining or stagnant yields or delayed canopy closure are subtle clues that should raise suspicion of SCN. Confirmation during July of the soybean year can be made by visual inspection of soybean roots for the presence of white females. Diagnosis at other times or during the rotation year must be made from soil tests conducted in a laboratory.