Due to its effect on the expansion rate of the Universe during Big Bang nucleosynthesis (BBN), the theoretical expectations for the primordial abundances of light elements depend on N_ν. Astrophysical measurements of the primordial ⁴He and ²D abundances lead to a value of N_ν = 3.14_-0.65 at 68% c.l., in very good agreement with the Standard Model expectation.