He is ill, said his government – at first. Then contrary statements denied that he was ill, or that he was ill but not seriously so, though all levels of government refused to go into detail, so spurring further speculation still.
By Thursday the most credible reports placed him in a Brussels hospital best known for treating blood cancers, undergoing treatment for a condition on the wrong side of serious, but with no clear prognosis.
The fate of Zenawi is of more than passing interest to a significant swath of Africa, as well as to the United States and incoming African Union head Nkosazana Dlamini-Zuma.
Loved by some, loathed by many, Zenawi has kept control of Ethiopia for more than two decades, seeing off Islamist rebels and keeping the country relatively stable amid the chaos that engulfed Somalia, Eritrea, and threatens to worsen along the border between Sudan and South Sudan.
While his tactics of intimidation and persecution of opposition figures won him few accolades, his willingness to go to war with al-Qaeda aligned forces in the region won him the support of Western powers.
He was due to remain in office until 2015.
There is no clear line of succession for the top post.
His wife, Azeb Mesfin, has been mooted as a successor, but at least three other high-ranking officials are also thought to be in the running.
Each has sway over different constituencies within the ruling Ethiopian People's Revolutionary Democratic Front.
But diplomats have been loath to make any predictions on success.
"It's a big-man situation," said one. "After so long it's difficult to imagine anybody else in control."