Castro has not appeared in public since his surgery.
Questions about whether he would be well enough to appear this week have dominated the run-up to the celebrations. Some guests said they feel more like a farewell than a birthday party. Castro's birthday was on August 14, but celebrations were delayed due to his ill health.
Most analysts agree that a successor government led by his brother and designated heir, Raul Castro, is in place.
Government sources say Raul, the world's longest-serving defence minister, and acting president, has been holding dozens of meetings, strengthening the ruling Communist party and coming to grips with Cuba's economic problems.
An Asian diplomat in Havana said: "It makes little difference if Fidel shows up or not. The succession has begun.
"Many people got it wrong. They thought Cuba would fall apart. But Cubans are not pushing for political change. They want more cheese and ham."