Self-assessment is promoted as an ideal form of assessment, particularly for adult learners as they need to be able to make judgements about how well they are doing something--whether it is related to learning, work or social interactions. However, there is also opposition to summative self-assessment on the grounds that students cannot validly and reliably assess their own work. At Massey University students enrolled in adult education qualifications are offered the opportunity to self or peer assess. This small-scale project investigated 472 student responses to self-assessment in this context. Findings show that 38% self-assessed by making comments on their work, and 25% awarded themselves a grade. A statistical analysis showed there was no significant difference (p greater than 0.01) between the self-assessed and teacher-assessed grades. Data also showed that higher achieving students tended to underrate and lower achieving to overrate. However, it is suggested that this may be a function of the grading scale rather than necessarily reflecting students' capability to self-assess. Some tensions and dilemmas around optional self-assessment are identified and discussed. (Contains 2 figures and 2 tables.)