Objective: Existing measures of needs in severe mental illness have been developed mainly from professionals’ viewpoints and are Eurocentric. Our aim was to standardize a measure of the needs of people with schizophrenia across several cultures and based on users’ own viewpoints. Method: An instrument to measure needs, based on qualitative data on users’, carers’ and professionals’ views, was tested in 164 people with schizophrenia or related psychoses in six countries. Participants underwent face-to-face interviews, one third of which were repeated 30 days later. Principal axis factoring and Promax rotation evaluated scale structure; Horn’s parallel combined with bootstrapping determined the number of factors; and intra-class correlation assessed test-retest reliability. Results: The instrument contained four factors: (1) health needs; (2) work and leisure needs; (3) existential needs; and (4) needs for support in daily living. Cronbach’s α for internal consistency was 0.81, 0.81, 0.77 and 0.76 for factors 1–4 and 0.81 for the scale as a whole. Correlation between factors was of moderate range for the first three factors (0.41–0.50) and low for the fourth factor (0.14–0.29). Intra-class correlation coefficient for test-retest reliability was 0.74 (0.64–0.82) for the whole scale. Mean item score on needs for support in daily living was lower than for the other factors. Conclusions: The MARISTÁN Scale of Needs evaluates needs from the patient perspective and it is a valid instrument to measure the needs of people with severe mental illness across cultures.