  In recent years new observations of pre-main sequence stars (pre-MS) with Z
<= Zsun have been made available. To take full advantage of the continuously
growing amount of data of pre-MS stars in different environments, we need to
develop updated pre-MS models for a wide range of metallicity to assign
reliable ages and masses to the observed stars. We present updated evolutionary
pre-MS models and isochrones for a fine grid of mass, age, metallicity, and
helium values. We use a standard and well-tested stellar evolutionary code
(i.e. FRANEC), that adopts outer boundary conditions from detailed and
realistic atmosphere models. In this code, we incorporate additional
improvements to the physical inputs related to the equation of state and the
low temperature radiative opacities essential to computing low-mass stellar
models. We make available via internet a large database of pre-MS tracks and
isochrones for a wide range of chemical compositions (Z = 0.0002 - 0.03),
masses (M = 0.2 - 7.0 Msun), and ages (1 - 100 Myr) for a solar-calibrated
mixing length parameter \alpha (i.e. 1.68). For each chemical composition,
additional models were computed with two different mixing length values, namely
\alpha = 1.2 and 1.9. Moreover, for Z >= 0.008, we also provided models with
two different initial deuterium abundances. The characteristics of the models
have been discussed in detail and compared with other work in the literature.
The main uncertainties affecting theoretical predictions have been critically
discussed. Comparisons with selected data indicate that there is close
agreement between theory and observation.
