Self-guided internet-delivered cognitive behavior therapy (iCBT) has considerable public health potential for treating anxiety and depression. However, no research has examined the use of self-guided iCBT, that is, treatment without contact with a clinician, specifically for older adults. The aim of the present study was to undertake a preliminary examination of the acceptability, efficacy and health economic impact of two entirely self-guided iCBT programs for adults over 60 years of age with anxiety and depression. Two separate single-group feasibility open trials of self-guided iCBT were conducted, the Anxiety Trial (n = 27) and the Depression Trial (n = 20), using the control groups of two randomized controlled trials. The online treatment packages consisted of five online educational lessons, which were delivered over 8 weeks without clinical contact. Participants rated the interventions as acceptable with more than 90% reporting the course was worth their time and more than 70% of participants completing at least 3 of the 5 lessons within the eight weeks. Significant reductions on measures of anxiety (Generalized Anxiety Disorder 7-item; GAD-7) and depression (Patient Health Questionnaire 9-item; PHQ-9) were observed from pre-treatment to post-treatment in both the Anxiety Trial (GAD-7 Cohen's d = 1.17; 95% CI: 0.55 to 1.75) and the Depression Trial (PHQ-9 Cohen's d = 1.06; 95% CI: 0.33 to 1.73). The economic analyses indicated that there was statistically significant improvement in health-related quality of life compared to baseline and marginally higher costs associated with treatment for both the Anxiety Trial ($69.84; 95% CI: $4.24 to $135.45) and the Depression Trial ($54.98; 95% CI: $3.84 to $106.12). The results provide preliminary support for the potential of entirely self-guided iCBT for older adults with anxiety and depression and indicate larger scale and controlled research trials are warranted.