Trichlorides of the lanthanide elements Ln=Ce-Lu form : (a) isotypic hexahydrates LnCl(3). 6H(2)O with a coordination number (CN) 8 for the Ln(3+) ions. (b) Two isotypic groups of trihydrates LnCl(3). 3H(2)O, in the first group Ln=Ce-Dy the CN is 8; the structure of the second group Ln=Er-Lu is unknown. With Ho no trihydrate exists; a dihydrate is formed. (c) Two isotypic groups of monohydrates LnCl(3). H2O with unknown structure - Ln=Ce-Dy and Ln=Ho-Lu. For all compounds and for anhydrous chlorides LnCl(3) solution enthalpies were measured with an isoperibolic calorimeter. The Delta(sol)H(0) values do not depend only on the difference (lattice enthalpies/hydration enthalpies), but also on the state in solution. According to Spedding the CN of the Ln(3+) ions against water changes from 9 to 8 between Nd and Sm, causing minima in the series of solution enthalpies. Dihydrates LnCl(3). 2H(2)O are found for Ln=Ce, Pr, Nd, Sm and presumably for Eu and Gd. They are not yet well characterised.