The Syrian Observatory for Human Rights listed 27,410 civilians, 9,800 soldiers and 1,359 military deserters as among those killed since the uprising began on March 15, 2011.
The Britain-based watchdog regards citizens who have taken up arms against Assad as civilians.
Observatory chief Rami Abdel Rahman said another 543 persons who could not be identified needed to be added to the figure, for a total of 39,112.
Even these figures are short of the real total, because they do not include people who have disappeared, many of whom are presumed dead, and deaths among the pro-regime “shabiha” militias.
And Abdel Rahman added that it is difficult to get accurate figures on both army and rebel deaths, “because both sides tend to minimise their losses.”
The Observatory relies on a countrywide network of activists and medics in civilian and military hospitals for its numbers.