Context : In recent years new observations of pre-main sequence stars ( pre-MS ) with \mathrm { Z } \leq \mathrm { Z } _ { \odot } 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 .

Aims : We present updated evolutionary pre-MS models and isochrones for a fine grid of mass , age , metallicity , and helium values .

Methods : 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 .

Results : We make available via internet a large database of pre-MS tracks and isochrones for a wide range of chemical compositions ( \mathrm { Z } = 0.0002 - 0.03 ) , masses ( M = 0.2 - 7.0 M _ { \odot } ) , 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 \mathrm { Z } \geq 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 .

Conclusions :