This paper summarizes the results of three studies of bias in patient satisfaction questionnaires due to acquiescent response set (ARS), a tendency to agree with statements of opinion regardless of content. Three independent surveys (N = 1,280) were fielded using the Patient Satisfaction Questionnaire. Across the three field tests, 40 to 60 per cent of respondents manifested some degree of ARS and from 2 to 10 per cent demonstrated noteworthy ARS tendencies. Occurrences of ARS accounted for significant upward bias in satisfaction scores computed from favorably worded questionnaire items and scales constructed from those items and significant downward bias in scores computed from unfavorably worded items and scales constructed from those items. These biases were greatest for groups reporting lower educational attainment or less income. An example was presented to show that mean satisfaction scores for groups differing in education were biased by ARS to such an extent that group differences in satisfaction were overestimated by favorably worded items and were missed entirely by unfavorably worded items. Balanced satisfaction scales, i.e., those containing both favorably and unfavorably worded items, were not correlated or correlated only slightly with ARS; therefore, group means for balanced scales were not biased by ARS or were biased only slightly.