All members of the chemical group of phthalates are salts of phthalic acid and in the international literature dealing with phthalates, the chemical group seems to have been regarded as phthalic acid diesters only, although, the diesters might be degraded to phthalic acid monoesters and phthalic acid. PDEs are widely used in a range of different products such as in, cardboard, paint, ink, adhesives, perfumes, but mainly as plasticisers in polyvinyl chloride (PVC) plastics. They are not chemically bound to the products and are therefore able to migrate to the aquatic environment. Biodegradation is considered to be the most significant fate process for phthalate diesters (Staples et al., 1997) and degradation of phthalate diesters to monoesters has been shown to occur in both aerobic (Inman et al., 1984; Shelton et al., 1984) and anaerobic (Ejlertsson et al., 1996) laboratory studies. Together with the diesters also the monoesters and phthalic acid has been found in old landfills with methanogenic leachates collected from different European landfills (Jonsson et al., 2002a). Results from laboratory scale landfill simulated reactors have showed that the major transformation of diesters to monoesters and PA was dedicated the early methanogenic phase (Jonsson et al., 2002b). In this study leachates from young landfill cells have been sampled at eight occasions during a period of two years (1998-2000). The cells have been constructed yearly i.e., 1995, 1996 and 1997, from ca. 10.000 metric tons of compacted but not grained municipal solid waste during a two months period. The well-defined starting period made it possible to study the development from acidogenic phase to methanogenic degradation by measuring pH, volatile organic acids (VFAs) and total organic carbon (TOC). This study present concentrations of the monoesters monomethyl, monoethyl, monobutyl, monobenzyl, mono(2-ethylhexyl) and didecyl phthalate (MMP, MEP, MbutP, MbenzP and MEHP respectively) and the diesters dimethyl, diethyl, dibutyl, butylbenzyl, and di(2-ethylhexyl) phthalate (respectively designated DMP, DEP, DBP, BBP, and DEHP), as well as phthalic acid and discuss the observed results from the laboratory lysimeter study.