Psychological treatment of insomnia has focused on primary insomnia (i.e., having a psychological origin). Secondary insomnia, sleep disturbance caused by a psychiatric or medical disorder, although it is more common than primary insomnia, has received very little attention as a result of the belief that it would be refractory to treatment. The present study randomly assigned older adults with secondary insomnia to a treatment group, 4 sessions composed of relaxation and stimulus control, or a no-treatment control group. Self-report assessments conducted at pretreatment, posttreatment, and a 3-month follow-up revealed that treated participants showed significantly greater improvement on wake time during the night, sleep efficiency percentage, and sleep quality rating. The authors hypothesize that treatment success was probably due in part to difficulty in diagnostic discrimination between primary and secondary insomnia.