Consent to research with decision-making capacity for research (DMC-R) is normally a requirement for study participation. Although the symptoms of schizophrenia and related psychoses are known to affect decision-making capacity for treatment (DMC-T), we know little about their effect on DMC-R.AimsWe aimed to determine if DMC-R differs from DMC-T in proportion and associated symptoms in an in-patient sample of people with schizophrenia and related psychoses. Cross-sectional study of psychiatric in-patients admitted for assessment and/or treatment of schizophrenia and related psychoses. We measured DMC-R and DMC-T using 'expert judgement' clinical assessment guided by the MacArthur Competence Assessment Tool for Clinical Research, the MacArthur Competence Assessment Tool for Treatment and the legal framework of the Mental Capacity Act (2005), in addition to symptoms of psychosis. There were 84 participants in the study. Half the participants had DMC-R (51%, 95% CI 40-62%) and a third had DMC-T (31%, 95% CI 21-43%) and this difference was statistically significant (P < 0.01). Thought disorder was most associated with lacking DMC-R (odds ratio 5.72, 95% CI 2.01-16.31, P = 0.001), whereas lack of insight was most associated with lacking DMC-T (odds ratio 26.34, 95% CI 3.60-192.66, P = 0.001). With the exception of improved education status and better DMC-R, there was no effect of sociodemographic variables on either DMC-R or DMC-T. We have shown that even when severely unwell, people with schizophrenia and related psychoses in in-patient settings commonly retain DMC-R despite lacking DMC-T. Furthermore, different symptoms have different effects on decision-making abilities for different decisions. We should not view in-patient psychiatric settings as a research 'no-go area' and, where appropriate, should recruit in these settings.Declaration of interestNone.