Officially, Chernobyl made 60 direct victims (Soviet records), but one is rather convinced that about 300 people died of radiation illness. The IAEA bases its estimates of victims on the measurements of contamination over the territory, with known activity-dose relationships, and basing itself upon the linear dose-effect hypothesis (5.6% chance to devellop a deadly cancer over 50 years per Sievert of dose). The linear dose-effect hypothesis is not established, but it is about the most severe hypothesis that one can make. In principle, it will be almost impossible to find out by epidemiology if there were any victims due to Chernobyl, as the *deadly* cancer rate increase will be in the noise.
Now, it is true that Greenpeace, and the German Green party ordered different reports, and one of them is the TORCH report, which assigns several illnesses to the low doses of Chernobyl: heart attacks, digestion problems... by epidemiological analysis (without reference study). They speak of about 400 000 victims, but on a completely unscientific basis. There has never been any indication of these kinds of illnesses as a result of low doses.
Also, a big part of the victims is due to extremely bad handling of the situation at Chernobyl. The nearby town was only evacuated 36 hours after the accident, and people have been sent to clean up the site without the slightest form of protection. They make the bulk of the 10 000 victims on long term and of the 300 victims on short term. If the accident were handled a bit more seriously, probably the number of victims would have been much lower and in the hundreds or a few thousand.