Objective: The relationship between cannabis use and psychosis has been studied intensively. However, few data are available on the relationship between cannabis use, ultra high risk for developing psychosis and neurocognition. The aim of the present study is to investigate the relationship between cannabis use, ultra high risk symptoms and cognitive functioning in ultra high risk patients and healthy controls. Methods: 63 Ultra high risk patients (34 cannabis users) and 58 control subjects (28 cannabis users) were assessed with clinical measures and a neuropsychological test battery. Patients were eligible for the study if they were between the ages of 12 and 35years and if they fell in one or more of the following inclusion groups: familial risk and reduced functioning, attenuated psychotic symptoms, brief limited intermittent psychotic symptoms and basic symptoms. Control subjects were eligible for the study if they were between the ages 12 and 35, had no present or past psychiatric illness, no family history of psychiatric illness, no drug use in the non cannabis using group and use of at least 4 joints per week in the cannabis using control group. Results: In the UHR and the control group, cannabis users experienced more basic symptoms and UHR symptoms than the non cannabis users. Moreover, cannabis users in the control group performed at the level of the UHR subjects on a test of verbal memory and verbal fluency. Frequency of cannabis use correlated with UHR and basic symptoms. Conclusions: Our results show that cannabis using UHR patients have more basic symptoms than non using patients. In addition healthy cannabis users have more subclinical UHR and basic symptoms and more neuropsychological dysfunctions than non cannabis users. Our results show that more frequent cannabis use is related to increased severity of basic and UHR symptoms.