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The physical structure of the envelopes around a sample of 14 massive young stars is investigated using maps and spectra in submillimeter continuum and lines of C17O, CS, C34S, and Nine ofH2CO.the sources are highly embedded luminous (103È105 young stellar objects that are bright near-L _ infrared sources but weak in radio continuum; the other objects are similar but not bright in the near-infrared and contain hot-core ÏÏÈtype objects and/or ultracompact H II regions. The data are used to constrain the temperature and density structure of the circumstellar envelopes on 102È105 AU scales, to investigate the relation between the dierent objects, and to search for evolutionary eects. The total column densities and the temperature proÐles are obtained by Ðtting self-consistent dust models to sub-millimeter photometry. The calculated temperatures range from 300 to 1000 K at D102 AU and from 10 to 30 K at D105 AU from the star. Visual extinctions are a few hundred to a few thousand magnitudes, assuming a grain opacity at 1300 km of B1 cm~2 g~1 of dust, as derived earlier for one of our sources. The mid-infrared data are consistent with a 30 % decrease of the opacity at higher temperatures, caused by the evaporation of the ice mantles. The CS, C34S, and data as well as the submillimeter dustH2COemission maps indicate density gradients n P r~a. Assuming a constant CS abundance throughout the envelope, values of a \ 1.0È1.5 are found, which is signiÐcantly Ñatter than the a \ 2.0 ^ 0.3 generall