Lipoprotein levels are currently recognized as independent risk factors for long-term cardiovascular events after acute myocardial infarction (AMI). During the acute-phase reaction after AMI, previous studies have reported trends of decreased low-density lipoprotein cholesterol (LDL-C), increased triglycerides, and variable high-density lipoprotein cholesterol (HDL-C) levels. However, the association between LDL-C and HDL-C levels and in-hospital mortality has not been well established following AMI. The relationship between lipid levels and in-hospital all-cause mortality in 115,492 patients hospitalized for AMI (July 2002 to December 2006), registered in the National Registry of Myocardial Infarction (NRMI) 4b–5, was evaluated using multivariable-adjusted logistic regression models. Mean LDL-C was 104 ± 38, HDL-C was 41 ± 14, and triglycerides 143 ± 83 mg/dl. Compared with the lowest quartile of LDL-C (<77 mg/dl), the risk of in-hospital mortality in the second to fourth quartiles was decreased (adjusted odds ratio 0.79, 0.80, and 0.85, respectively). For HDL-C, only those in the lowest quartile (<31 mg/dl) had higher risk of in-hospital mortality (odds ratio 1.20) compared with the highest quartile (≥47 mg/dl). Results from NRMI 4b–5 suggest a lipid paradox, with lower LDL-C levels associated with increased risk of in-hospital mortality, contrary to findings outside the acute setting. Consistent with previous analyses, lowest HDL-C levels were associated with increased in-hospital mortality. In conclusion, further explorations of the relationship between very low levels of LDL-C, myocardial necrosis, and subsequent adverse cardiovascular events are warranted.