The Process Density Index (PDI), originally developed by Edwards, is a potentially useful metric for assessing phonological development that is based on the average number of phonological process applications per word in a speech sample. The purpose of the present study was to gather PDI reference data for Dutch-speaking children. Speech samples were collected and the PDI values were determined in 120 Dutch-speaking children aged between 2;6 and 5;6 years of both genders. Boys showed a higher PDI than girls, and there was a strong negative relationship between age and PDI. The presence of a history of otitis media, socioeconomic status, and sibling status, however, were of no influence. The results confirm trends seen in previous studies on phonological development of typically developing children using other metrics. This suggests that the PDI is a valid measure to assess phonological acquisition.