Presenting Author details:else.marie.loeberg@psych.uib.no Sandviksleitet 1, 5035 Bergen, Norway, Tel.: +47 98 094420. Background: A history of cannabis abuse in schizophrenia and schizophrenia-like psychoses may indicate a subgroup with a different neurodevelopmental course. We present data from a study on neurocognitive functioning in this patient group with and without a history of cannabis abuse (can+ and can−), in addition to preliminary data from an ongoing study on neurocognitive changes over time in these groups. Methods: Study A: A heterogeneous group of 31 schizophrenic patients where split into can+/can− groups based on patient's records, a therapist's questionnaire, and Structured Clinical Interview (SCID) interviews and compared on a comprehensive neuropsychological test battery, clinical and demographic data. Study B: 26 patients with acute schizophrenia or schizophrenia-like psychoses were examined at admission, after 6 weeks and 3 months. They were split into can+/can− groups based on patient's records and Clinician Drug Use Scale, validated through urine samples. They were compared on neuropsychological functioning (neuropsychological screening test at admission and 6 weeks, comprehensive battery at 3 months) and clinical and demographic data. Results: Study A: The can+ group performed better than the can− group in regard to general abilities, executive functions, attention/working memory and psychomotor speed. Furthermore, the can+ group showed a 4-year younger onset age. Study B: The can+ group showed a different dynamic of neurocognitive functioning over time than the can− group, with larger improvements of their neurocognitive functioning. Conclusions: Both studies suggest a lower neurocognitive vulnerability load in the can+ group. In this group, cannabis abuse, more than neurocognitive vulnerability, may trigger the neurocognitive and psychotic breakdown seen at the acute state. Such a cannabis-induced breakdown may also explain the earlier onset age in this group.