A generic programme of behavioural modification for the clinical treatment of separation-related behaviours in dogs was assessed in a controlled replicated trial. After 12 weeks of treatment, 56 per cent of the owners of the treated dogs reported significant improvements in their dogs’ behaviour, and a further 25 per cent reported a slight improvement. The owners’ reports were generally supported by changes in the behaviour of the dogs as recorded on video when they were left alone. The majority of the untreated dogs continued to show the same degree of separation-related behaviour throughout the 12 weeks of the trial. In a supplementary set of 30 case studies, treated with a behavioural programme tailored to the specific diagnosis for each dog, all the owners reported improvements in their dogs’ behaviour after 12 weeks of treatment.