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Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous organic contaminant derived mainly from incomplete combustion of organic materials and natural processes. As a result of its acute toxicities to humans at low concentration, the United States Environmental Protection Agency has included PAHs in its priority pollutants list and recommends their routine monitoring in water samples. This study investigates 17 parents PAHs in water samples from Lagos lagoon. Extraction was carried out by liquid-liquid extraction method and quantification with Gas-chromatograph coupled to Flame ionization detector. It was noted that 31.5 % of samples analyzed, were positive for PAHs. The mean concentrations of PAHs for samples collected at the surface (0.5m depth) and bottom (2.5m depth) varied from ND- 9.8 and ND- 7.9 µg/L respectively. The mean concentration of PAHs in 28.8 % of samples analyzed were sufficiently high (> 0.01µg/L) to cause acute toxicity to the exposed organisms. The mean concentrations of PAHs in this study (ND-5.73 µg/L) were higher when compared with results of previous analyses of water samples from the same lagoon (non-detectable to 3.73 µg/L). The outcome indicates the persistence and bio-accumulative nature of the chemicals in this particular aquatic environment and hence the need for regular monitoring of the lagoon to avert consequent health effects on exposed organisms and man