Since its discovery in the United States, the invasive plataspid Megacopta cribraria (F.) (Hemiptera: Plataspidae) has infested soybean [Glycine max (L.) Merrill] fields in often alarming numbers in parts of the southeastern United States. Although a known feeder on soybean, reports of its pest status in its native Asian range are conflicting, and little information exists documenting its impact on soybean yields. Our objective was to examine the relationship between M. cribraria density and soybean yield loss. M. cribraria adults and nymphs were confined to small soybean plots by using walk-in field cages from late vegetative stage to harvest in 2011 and 2012. Adults (0, 5, or 25 per plant) were added at late vegetative stages, and their progeny were allowed to complete a full generation within the caged plots. Densities reached as high as 182.5 ± 23.1 (SEM) nymphs and adults per plant, and soybean yield was reduced by as much as 59.6% at the highest density treatment. The yield components seeds per pod and individual seed weight were reduced as M. cribraria densities increased, but pods per plant and protein and oil content were not affected. Preliminary economic injury level curves for a range of grain prices and management costs were calculated based on 2012 yield loss data combined with population monitoring. M. cribraria is capable of causing severe reductions in soybean yields at densities that are relevant within its invasive U.S. range.