To evaluate whether the Delirium Diagnostic Tool-Provisional (DDT-Pro), a 0-9 point scale with three items each representing symptoms from delirium's three core domains, differentiates subsyndromal delirium (SSD) from delirium and no delirium.We applied cluster analyses of DDT-Pro scores from 200 consecutive inpatients using three reference standards for delirium diagnosis to determine DDT-Pro cutoff values for delirium, SSD and no delirium groups. Clinical validators and DDT-Pro item scores were compared among groups.DDT-Pro SSD range was 6-7 (n = 54), with no delirium having higher scores (n = 98) and delirium lower (n = 48). Dementia prevalence in the SSD group (40.7%) was intermediate between no delirium (20.4%) and delirium (66.7%). SSD and delirium groups were more affected than no delirium regarding medical comorbidities, hospital stay (no delirium 1 week) and mortality (SSD = 7.4%, delirium = 18.8%, no delirium = 1%). Values for motor subtypes, frontal lobe signs, and DRS-R98 in the SSD group were intermediate between no delirium and delirium, as well as for the DDT-Pro items (all p < 0.05).All DDT-Pro items, which represent the three delirium core domains, are important for SSD diagnosis. Patients scoring in the SSD 6-7 range have significant clinical and prognostic features and deserve clinical attention.