Indefinitely. No maximum. As long as the doctor says

I work in Spain, happen to be on sick leave/disability, and that's not exactly correct:

• The doctor can only authorize 365 days of paid sick leave
• After that, you get back to your company's health insurer ("mutua") who has 180 days of paid sick leave to either:
  • Treat you until you're healed (or claim you're healed) and put you back to work (if you refuse, you get fired)
  • Grant you permanent disability

If the insurer decides that you're healed, you can't go back onto a sick leave for the same reason for... I think it's 6 months.