We present a new analysis of nanoscale lattice defects observed after low-dose in situ self-ion irradiation of tungsten foils at cryogenic temperature. For decades, defect counts and size-frequency histograms have been the standard form of presenting a quantitative analysis of the nanoscale “black-dot” damage typical of such irradiations. Here we demonstrate a new statistical technique for generating a probability distribution for the number of defects produced in a single cascade. We show that while an average of fewer than one defect is observed per incident ion, the number of cascades with two or more visible defects produced is significant.