A vacuum cleaner comprises a cyclonic separator having a first cyclone and a plurality of downstream secondary cyclones. The first cyclone comprises a side wall defining a first cyclonic chamber, and the secondary cyclones each comprise a side wall defining a second cyclonic chamber. A dirt cup assembly is mounted below the cyclonic separator to collect contaminants separated in the first and second cyclonic chambers. The secondary cyclones can be arranged around the first cyclone side wall and form a gap between adjacent secondary cyclones so that the first cyclone side wall is exposed at the gap. A working air conduit can extend through the first cyclone and the dirt cup assembly to couple the secondary cyclones to a suction source located below the dirt cup assembly. Furthermore, the secondary cyclones can have a vortex stabilizer.