The study aimed at evaluating the diadochokinetic (DDK) skills of Greek-speaking preschool children with phonological disorder (PD) by means of a structured evaluation protocol and at proposing cut-off points for children at risk of speech impairment. The participants were 36 children with PD and 60 typically developing (TD) peers. The groups were matched on age and gender. The PD group performed significantly slower than the TD group in all speech DDK tasks but not in the oral-motor tasks. The ROC analysis showed a statistically significant positive discrimination for all speech tasks. The internal consistency of the protocol was excellent (Cronbach's [alpha] = 0.844), while complex stimuli showed a better discriminatory ability. The obtained results agree with Dodd's classification for speech sound disorders (SSDs). Different types of speech stimuli must be included in the evaluation of DDK performance as a clinical predictor for preschoolers with SSDs who face difficulties in speech maturation.