Based on observations of HII regions and on the new computations of the recombination coefficients of the HeI lines by Porter el al. we obtain a primordial helium abundance by mass of Y_P = 0.2446 ± 0.0029. We consider thirteen sources of error for the Y_P determination; some of them are mainly due to systematic effects, while the rest are mainly due to statistical effects. We compare our results with other determinations of Y_P present in the literature. Combining our Y_P value with computations of primordial nucleosynthesis we find a number of neutrino species {N_{eff}=2.90± 0.22}, and a neutron mean life τ_{ν}=872± 14s.