You employers reassurance was just that  - a reassuring comment. It was not a legally binding contract.  However, the fact is that if you were out on FMLA (you did not indicate) then you cannot be fired simply for being out sick.  That having been said, if your termination was due another reason unrelated to your illness (a job performance issue or the like)then yes it was legal to let you go.  If you were not out on FMLA (or equivalent state leave), then your employer had full discretion as to whether or not to continue your employment with the company.  As a general rule an employer can hire/fire an employee for any reason or no reason at all.  That is, so long as the employee is an "at will" employee.  Therefore, in your situation, unless you had an employment contract or union agreement to the contrary, or this action violated company policy, or was the result of discrimination, you have no claim.  While one form of discrimination is treating someone differently based on a disability, it's not clear from your question whether your medical condition arises to the level of a legally actionable disability.  Since the specifics of your case are not clear, you really should discuss your situation directly with an employment law attorney in your area.