Insights into determination of study participation are useful for researchers, clinicians and for ethical considerations. Few large-scale genomic studies have involved motives for enrollment, in schizophrenia patients and unaffected controls. In a case-control study with participants recruited nation-wide in Sweden between 2005 and 2010, semi-structured interviews on motives and attitudes towards future studies were explored in 2767 schizophrenia cases and 4466 controls. In qualitative and quantitative analyses, we identified altruism as a major determinant in 84% of the cases and in 97% of the controls. Among pre-defined subcategories of altruism, cases with schizophrenia were more often referring to science for example, 'I want to help science move forward' or 'I want better medications for future generations' in relation to unaffected controls that were more often referring to common humanity such as 'It is my duty and responsibility to help'. In schizophrenia, motives related to personal benefit and social influence were reported by 9% and 5%. We conclude that individuals with schizophrenia frequently report altruistic motives for study participation, almost to the same extent as unaffected controls. In contrast to unfortunate stereotypes, people with schizophrenia wish others to benefit from their experiences with severe mental illness and should not be refrained from participating in genomic research.