Anaerobic digestion of two kinds of reconstituted municipal solid waste (MSW) was followed in laboratory scale experiments in order to obtain a carbon mass balance. Despite the complexity of the initial MSW matrix, triplicate reactors showed a reasonable level of reproducibility. Under water saturated conditions, recorded methane yields were important : 178 and 126 m3 of CH4/ton of dry waste I (mean French MSW composition) and II (compost replaced putrescibles), respectively. The carbon distribution at the end of the waste I degradation, without taking into account the carbon coming from the initial leachate, was : 30.7% ± 3.5% as mineralized fraction (TIC and CO2), 28.6% ± 2.8% as valorized fraction (CH4), 7.9% ± 2.5% as solubilized fraction (TOC) and 33.8% ± 3.8% as solid fraction. The carbon distribution for waste II was different : 22.7% ± 3.1% as mineralized fraction, 24.6% ± 1.1% as valorized fraction, 3.6% ± 2.0% as solubilized fraction and 49.1% ± 2.9% as solid fraction.