Aliphatics (n-alkanes) and polycyclic aromatic hydrocarbons (PAHs) were measured in surface sediments collected from 12 sampling points (P1–P12) of sewage discharge to the sea from the wastewater treatment plant of Cortiou (France). Total n-alkanes and PAHs concentrations ranged from 34 to 2,155 and 696 to 10,700 μg kg−1, respectively. Some specific hydrocarbon indexes suggested that terrestrial biogenic inputs are predominant compared to marine sources and that pyrolytic sources derived from wood and biomass combustion contribute to PAHs in the surface sediments. Total linear alkyl benzenes in Cortiou sediments ranged from 42.9 to 502.3 μg kg−1. Low internal and external (I/E) isomers ratio (P0) suggests that inadequately treated sewage is discharged into the marine environment while some environmental processes might change I/E ratios during transport seaward (P1–P12). The high contaminant levels followed by the cumulative concentration of several compounds may lead to elevated toxicity levels in the sediments.