Operating in the unlicensed 2.4-GHz ISM band, a Bluetooth piconet will inevitably encounter the interference problem from other piconets. With a special channel model and packet formats, one research issue is how to predict the packet collision effect in a multi-piconet environment. In an earlier work (El-Hoiydi (2001)), this problem is studied, but the result is still very limited, due to the assumptions that packets must be single-slot ones and that time slots of each piconet must be fully occupied by packets. A more general analysis is presented in this work by eliminating these constraints.