Summarizes results of studies of bias in patient satisfaction questionnaires due to acquiescent response set (ARS), a tendency to agree with statements regardless of content. Three surveys (N=1280) were fielded using the Patient Satisfaction Questionnaire in which 40 to 60 percent of respondents manifested some degree of ARS and 2 to 10 percent demonstrated noteworthy ARS tendencies. ARS accounted for significant upward bias in satisfaction scores from favorably worded items and significant downward bias from unfavorably worded items. Biases were greatest for groups reporting lower educational attainment or less income. An example shows that mean satisfaction scores for groups differing in education were so biased by ARS that differences in satisfaction were overestimated by favorably worded items and missed by unfavorably worded items. Balanced satisfaction scales, (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 or biased only slightly.