Process for recovering at least 70% of hollow glass microspheres having an average diameter, according to the ASTM D1214-1989, ranging from 5 to 200 m contained in a mixture of drilling mud and cuttings which comprises: a) screening, if necessary, the mixture through one or more 5 to 20 mesh sieves; b) feeding the screened mixture to one or more cyclones and/or hydrocyclones arranged in series, each of which is fed with a volume flow-rate from 1.5 to 10 times higher than the maximum nominal operating value.