The effect of aging on pyrene transformation and pyrene association with fractions of the sedimentary organic matrix (SdOM) was evaluated using [4,9-(13)C2]pyrene. Sediments were collected from a site of previous petroleum hydrocarbon contamination (New Orleans, LA, USA). Aged sediments were autoclaved for 1 h, amended with pyrene, and then stored in the dark in a 0.05% NaN3 solution for 120 d. Both aged and nonaged sediments were incubated in aerated microcosms for 120 d. Microcosms were acidified to collect evolved carbon dioxide (CO2); sediments were fractionated and lipid extracted to quantify pyrene in SdOM fractions. Cross-polarization magic angle spinning 13C-nuclear magnetic resonance (CPMAS 13C-NMR) spectra indicated that synthetic aging techniques did alter SdOM structure to some degree, but these changes did not affect SdOM affinity for pyrene. Aging delayed pyrene mineralization and increased pyrene concentrations extracted from bulk sediment and humic fractions. Aging also reduced the toxicity of sediment humin. Pyrene-4,5-dione and pyrene cis-4,5-dihydrodiol were identified in extracts of aged sediments by 13C-NMR and gas chromatography mass spectrometry, respectively.