Background: The length of stay and bed usage on acute psychogeriatric admission wards are influenced by several factors. The impact of a dedicated specialist social worker working exclusively with acutely ill psychogeriatric inpatients and with a dedicated budget for domiciliary care packages on the length of stay, bed usage, and costs was evaluated in an opportunistic “before and after” cohort study. Method: The length of stay and bed usage for a 7-month period when a dedicated social worker and a dedicated budget for domiciliary care packages were implemented were compared with an identical 7-month period the year before. Costs incurred for extracontractual referral admissions (ECRs) were also calculated for the same periods. Results: The implementation of a dedicated specialist social worker with a dedicated budget for domiciliary care packages did not demonstrate a statistically significant reduction in length of stay, but bed usage was reduced in both the local National Health Service hospital and the ECR units. The costs incurred for ECR admissions were also reduced; this reduction in costs was similar to the cost of employing a dedicated specialist social worker with the domiciliary care package. Conclusions: A dedicated specialist social worker working exclusively with psychogeriatric inpatients with a dedicated budget for domiciliary care packages was demonstrated to be cost-effective in this study. Ideally, a multicenter, randomized, and controlled study of such an intervention should be undertaken to confirm these findings.