From 2009, Dr Diaz joined the Swedish program of uterus transplantation and was a part of the first team to obtain a live birth from a uterus transplantation in 2012. In 2013, Dr Diaz returned to Valencia and led the Valencian Program for Fertility Preservation, which is one of the most internationally recognized programs of fertility preservation for oncological patients. He was also part of La Fe University IVF program, the largest Spanish public IVF program, performing more than 2000 IVF cycles / year. He combined his medical duties in the field of fertility with his surgical activities at La Fe University Hospital within the fertility surgery unit and gynae-oncology units for national referral centers.
His main research interests are ovarian rejuvenation, fertility preservation, with a special interest in ovarian cortex transplantation, uterus transplantation and poor response in IVF. Within his fields of interest, he obtained several grants from the Spanish Ministry of Health and the Valencian Health Agency as well as from different private institutions. He is a former Associate Editor of Human Reproduction (2013-2016), and he has published more than 100 peer-reviewed scientific papers and book chapters.