There are currently no old-age specific interventions for autistic adults. Therefore, in this explorative study, we examined the possible effects of a co-designed psychoeducation program for older autistic adults (55+ years), with a multiple case study design ( N = 9, age 56–73 years; Netherlands Trial Register (code Trial NL5670)). For each participant, also a person close to them (a proxy) participated. This allowed us to calculate a discrepancy score regarding autistic traits and cognitive challenges. The main hypothesis was that our program, delivered after general psychoeducation, would result in a discrepancy reduction between self and proxy reports. However, contrary to our hypothesis, we observed neither intervention effects on our primary outcome measures (discrepancy scores) nor the secondary outcome measures (mastery, self-efficacy, self-esteem, self-stigmatization, quality of life, and hope and future perspectives). Thus, despite co-designing the current intervention, the results were not promising. However, the positive feedback and suggestions of the participants make developing an improved version of a specific psychoeducation program for older autistic adults still a worthwhile pursuit. Lay abstract After receiving an autism diagnosis by a clinician, psychoeducation (i.e. information regarding autism) is often offered. However, older autistic adults (55+ years) may need specific information about the challenges they face in daily life as they are in a specific life phase. A psychoeducation program for this specific age group does not exist yet. We first developed such a program together with autistic adults and clinicians working with autistic people, after which we tested the program with nine autistic adults (56–73 years) and someone close to them (so-called proxy). Before testing the program, we determined together with autistic older adults what they thought should be the outcome of this intervention in order to state whether it was, indeed, a useful intervention. Earlier studies found that autistic people often think differently about their own autistic characteristics than their proxy. A reduction of this difference could increase mutual understanding. Therefore, the main hypothesis was that the program would decrease this difference with respect to autistic characteristics and cognitive challenges (e.g. memory problems). Another hypothesis was that the program would have a positive impact on a series of other factors, such as self-esteem. The results showed that the program did neither decrease the difference in insight nor the other tested factors. Nonetheless, we believe it is important to keep on working on a psychoeducation program for older autistic adults, because participants informed us the program had still helped them in certain ways and they gave helpful feedback for improvements of the program.