A procedure is described to estimate the persistence length and related properties of a persistent polymer by MD simulations of a small fragment, including solvent effects. The procedure is applied to cellulose in aqueous solution, which leads to an upper limit of the persistence length of 145 +/- 10 Angstrom. The occurrence of small amounts of folded conformations seems to be indicated by comparison of the theoretical with experimental data. The behavior of the cellulose chain is consistent with the Kratky-Porod wormlike model.