On October 1, 2018, I visited a Mexican person who is in the business of helping qualified applicants join IMSS. She tells me that if you have ANY pre-existing condition, including high blood pressure, you will be rejected. Further, she says that one must join WITH a family member (spouse, child...). That means that both must pass the required physical exams. Before the exams, you pay the fee. Fail the exam and you lose the fee. It may have been true in 2016 that anyone could join but seems no longer to be the case. I double-checked the info with an attorney who confirmed. Since either person would make money by helping me join IMSS, I figure they would give it a try if they thought there was a chance. I'm healthy; my spouse is not. I wouldn't even try to sign him up and without him, I have no other family member who is a resident of Mexico. If you have a different and recent experience, please share.