Background Duration of untreated psychosis (DUP) has been significantly associated with poor clinical and social outcomes in First Episode Psychosis (FEP) patients, but an association with cognitive outcomes has not been clearly established. Method Seventy-seven consecutively admitted, drug-naïve patients with FEP were assessed at baseline and at 1month and 6months. Underlying dimensions of DUP (general prodrome and positive, negative and disorganisation symptoms) were assessed using the Symptom Onset in Schizophrenia (SOS) inventory (Perkins et al., 2000). To assess the effect of DUP on the neuropsychological status of the patients, a linear mixed-effect model was fitted to each neuropsychological dimension. These models included a dichotomised version of DUP (short versus long duration) as a fixed effect, several adjusting variables to account for patient differences, and a random effect to incorporate the longitudinal structure of the data. Results Patients with a short duration of untreated negative symptoms (DUNS) or a short duration of untreated positive symptoms (DUPS) outperformed patients with a long duration of untreated symptoms on memory tasks and a pre-attentional visual task but not on measures of verbal fluency, attention, reaction time, visual processing and executive functions. Conclusions This study provides additional support for an early intervention to shorten DUP to facilitate a better outcome in memory and attentional domains of FEP patients.