Psychiatric illnesses are prevalent in general hospitals and associated with length of stay (LOS). Liaison psychiatry teams provide psychiatric care in acute hospitals and can improve mental health-related outcomes but, to achieve ambitious policy targets, services must understand local need.

Using electronic patient records, we investigate associations between psychiatric diagnoses and LOS in South East London hospitals.

Patient records were extracted using the South London and Maudsley NHS Foundation Trust Biomedical Research Centre Case Register Interactive Search system. There were 6378 admissions seen by liaison psychiatry aged <65 years between 2011 and 2016. Linear mixed-effects models investigated the impact of psychiatric diagnoses on LOS. Potential confounders included medical diagnoses, gender, age, ethnicity, social deprivation, hospital site and investment per admission.

According to marginal means, longer LOS is associated with primary diagnoses of organic disorders (mean: 23 days, 95% CI 20.39–25.61), depressive disorders (mean: 11.03 days, 95% CI 9.74–25.61) and psychotic disorders (mean: 10.63 days, 95% CI 8.75–12.51). Shorter LOS is associated with personality disorders (mean: 6.28 days, 95% CI 4.12–8.45), bipolar affective disorders (mean 6.81 days, 95% CI 3.49–10.14) and substance-related problems (mean 7.53 days, 95% CI 6.01–9.05).

Psychiatric diagnoses have differential associations with in-patient LOS. Liaison psychiatry teams aim to mitigate the impact of psychiatric illness on patient and hospital outcomes but understanding local need and the wider context of care provision is needed to maximise potential benefits.

M.H. is a consultant liaison psychiatrist for King's College Hospital adult liaison psychiatry team. At the time of writing, H.T. was senior business manager at SLaM psychological medicine and integrated care clinical academic group. These may be considered financial and/or non-financial interests given the implications of findings for service funding.