This study examined the dimensions of burden perceived by key-relatives of patients suffering from schizophrenia spectrum disorder by the development of an instrument, the Family Burden Scale (FBS) and the underlying predictors. One hundred and seventy one primary caregivers, living with 158 patients suffering from chronic psychotic illness and maintained on community basis in Athens area, were interviewed by the use of FBS supplemented by the Family Atmosphere Scale and GHQ. Construction procedure and factor analysis of FBS produced a scale of 23 items in four factors, three of them measuring objective and the fourth one, subjective burden. The scale was also proved to be reliable and valid. Forty-five percent of primary caregivers reported high levels of burden. Psychological impairment (high GHQ scores) was related with high levels of burden and negative family atmosphere. Previous admissions and duration of illness were also found to predict burden. The results suggest that FBS differentiates objective from subjective burden. Psychological well being of carers is affected by the dimensions of perceived burden.