Our objective was to establish a mechanism for monitoring indicators of the state of health of inner London's mental illness services. Data were collected for a census week around 15 June 1994. Local data collection was coordinated by consultant pyschiatrists working in inner London services. Twelve services participated with a combined catchment population of 2.6 m. They included ten London services which were among the 17 most socially deprived areas of England. Main indicators were admission bed occupancy levels (including an estimate of the total requirement), proportion of patients detained under the Mental Health Act, number of assaults committed by inpatients, number of emergency assessments and CPN caseloads. The mean true bed occupancy (which reflects the number of patients who were receiving, or required, in-patient care on census day) was 130%. To meet all need for acute psychiatric care, including for patients who should have been admitted and those discharged prematurely because beds were full, a further 426 beds would have been required. Fifty per cent of patients were legally detained. Physical assaults were virtually a daily occurrence on the admission units. Average community pyschiatric nurse caseloads were 37, suggesting that the majority were not working intensively with limited caseloads of patients with severe mental illness. These indicators, although imperfect, will allow for some measurement of the impact of local and central initiatives on the poor state of London's mental illness services.