Thin and transparent poly(p-xylylene) (PPX) layers in the range 2-1550 nm have been prepared by means of chemical vapor deposition (CVD) via vapor-phase pyrolysis of the cyclic di-p-xylylene dimer. Ellipsometrical measurements are employed on those materials to study in detail the dependence of layer formation on sublimation temperature (80-140 degrees C) and deposition time (5-360 min). The layer growth rate on silicon wafers is found to be 0.3, 1.0, 6.3, and 11.8 mm/min at sublimation temperatures of 80, 100, 120, and 140 degrees C, respectively. The PPX layers are optically transparent in the investigated range of wavelengths from 190 to 1700 nm. Atomic force microscopy (AFM) studies show a surface roughness of 2-4 nm and larger values, 5-9 nm, at a high sublimation temperature of 140 degrees C or large deposition times t(dc) > 120 min. Wide angle X-ray diffraction (WAXD) experiments describe a monoclinic crystalline alpha-form with reflections (020) and (110) at 2 theta(Cu) = 17.7 and 22.8 degrees, respectively. Small angle X-ray scattering (SAXS) studies reveal a lamellar structure with a long period of 8.3 nm.