Backgrond: Pregnant women are at increased risk for complications from seasonal influenza. Early data suggest that influenza A (H1N1) may present an even greater risk. Case: We present the case of a pregnant woman with severe pulmonary complications from 2009 H1N1 whose care was further complicated by delay in diagnosis and unusual laboratory abnormalities. Conclusion: H1N1 may pose several diagnostic challenges for obstetricians, including increased rates of serious pulmonary complications, decreased sensitivity of rapid tests with delay in initiation of antiviral therapy, and abnormal laboratory findings usually associated with other complications of pregnancy. We document these problems, urge initiation of antiviral therapy based on clinical suspicion, and recognize the potential laboratory abnormalities that may be associated with severe influenza illness. © 2010 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins.