BACKGROUND Analysis of lipoprotein size and composition by nuclear magnetic resonance (NMR) has been advocated as a method for identifying individuals at high CVD risk. We compared risk stratification between NMR-based LDL particle number (LDL-PNUM), LDL-cholesterol (LDL-C), and apolipoprotein B (apoB). METHODS Retrospective data from patients with simultaneous orders for LDL-PNUM, LDL-C, and apoB were analyzed and included data from an NMR assay (Numares). Quantitative and qualitative analyses were performed. Additional lipid parameters were investigated for patients with discordant risk classifications in LDL-related measurements. The percent change of LDL-PNUM was compared to the percent change of LDL-C or apoB for patients with serial measurements. RESULTS We observed good quantitative and qualitative correlation when comparing LDL-PNUM to either LDL-C or apoB (Spearman's ρ ≥ 0.83, percent agreements ≥ 85%). Among the patients with discordant risk stratification, most had increased LDL-PNUM and normal LDL-C and apoB. For patients with serial measurements, a strong correlation between the LDL-PNUM percent change and the LDL-C or apoB percent change was observed (Spearman's ρ > 0.93). CONCLUSIONS For many patients, risk stratification of LDL-PNUM is similar to apoB or LDL-C using cut-offs proposed by guidelines.