King Juan Carlos of Spain successfully underwent surgery for herniated discs in his lower spine at a Madrid hospital on Sunday, the royal palace said.
The operation took about three hours and "proved entirely satisfactory," the palace said. It was the 75-year-old's fourth operation in 12 months, and the 12th time he has undergone surgery during his lifetime.
Neurosurgeon Manuel de la Torre, who performed the operation, told reporters that it would take between two and six months for the king to recover. The head of state would likely remain in the hospital for around a week, he said, adding that two of the king's spinal segments had been involved.
On his arrival at the La Merced clinic, the monarch lowered his passenger-side car window and said, "Here I am again," to journalists and television cameras gathered outside.
Juan Carlos had hip surgery last November and has suffered several other health issues in the past two years, including needing knee surgery and the removal of a benign lung tumor.
It has not been a good year for the king, who has largely been admired for his role in helping steer Spain to democracy after a long period of military dictatorship under General Francisco Franco.
The monarch's son-in-law, Inaki Urdangarin, who is married to the king's second daughter, Princess Cristina, is under investigation on suspicion of having used his position to embezzle several million dollars in public contracts assigned to a supposedly nonprofit foundation he set up.
And Juan Carlos was vilified last year after breaking his hip while on a luxurious African safari to hunt elephants at a time when ordinary Spaniards were being buffeted by an economy entering its second recession in three years.