my son has a green card since june 2015. he was here one month during summer and then he went back to Mexico to study he came back on december 8th and

Hello. A permanent resident is required to maintain permanent residence in the US to maintain their status.  Normally when a permanent resident leaves the US for a period of 6 months or more an officer can presume they have abandoned their status.  However, only an immigration judge can make that determination. If your son plans on being out of the US for periods of six months or more then I recommend he files for advance permission for reentry into the US.  If approved this would prevent any immigration officer from presuming your son has abandoned his status. There is more information regarding this issue as most situations are case specific. I would be glad to further discuss this matter with you personally. Please call my office for a free consultation. Samuel J. Zermeno, Esq. 915-219-4070 sjzermeno@zermenolaw.com www.zermenolaw.com