The aim of the investigation was to estimate the impact of the presence of chromium ions on decrease in PAHs concentration in sewage sludge stored under aerobic conditions. The studies were carried out using dewatered and biochemically stabilized sludges. The changes in the concentration of PAHs were followed in five series: in sludge samples taken after filter press (biotic samples—control samples), in sludge samples with added sodium azide (abiotic samples), in sludge with the addition of a standard PAH mixture, in sludge with added chromium(III) chloride, and in sludge with the addition of both the standard PAH mixture and Cr. The Cr was added into the sludges samples as a solution of chromium(III) chloride. The sludge samples were incubated for 12 weeks. Determination of PAHs in sludge samples was made at the beginning of the experiment (the initial concentration) and then six times over 2 weeks. The gas chromatography–mass spectrometry was used for qualification and quantification of PAHs. Six PAHs listed by EPA were identified: benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenzo(a,h)anthracene, benzo(g,h,i)perylene, and indeno(1,2,3,c,d)pyrene. In sludges taken from municipal treatment plant, the average PAHs concentration was 289 μg/kg d.m. The inhibition of PAH degradation was found in sludges supplemented with chromium chloride (final average PAH concentration in modified sludges was four times higher than in the control sample).