Definitions of Auditory Processing Disorder (APD) suggest that it is associated with localisation problems (ASHA Working Group on APD, 2005; BSA APD Interest Group, 2003); however, there appears to be little or no direct evidence for this link in the literature. The main aim of this project was to investigate whether poor localisation is in fact observed in participants with suspected APD (sAPD). Two studies were conducted on sAPD groups (age range 8 - 21 years in the pilot study and 7 - 12 years in the main study), characterised by normal pure tone audiometry, poor performance on the Children's Auditory Performance Scale questionnaire (CHAPS), parental concerns with education underperformance and referral to an APD out-patient clinic. Results were compared to matched control groups. In the pilot study N = 24 per group and in the main study N = 32: a total of 112 participants took part in the complete project. The aim of the project related to three linked hypotheses: • mean localisation performance of an sAPD group is significantly worse than that of a control group • localisation performance of some members of an sAPD group is below the normal range, as indicated by a control group • localisation performance ofmost or all members ofan sAPD group is below the normal range, as indicated by a control group The project involved preliminary work in several areas, including development of participant selection/screening procedures and development of measurement equipment, including a loudspeaker array and associated drive electronics. The localisation task involved 'click' stimuli with forced choice between numbered loudspeaker positions. Twenty-three loudspeakers were positioned at ear level to the participant, over a 1800 arc with a separation angle of 8.2 0 between adjacent loudspeakers. The main study was conducted in a similar fashion to the pilot study but included a noise distracter of multitalker babble, intended to provide a more challenging listening condition. Results from the pilot study confirmed that the basic experimental protocol was appropriate for measurement of localisation accuracy. The majority of the control group had r.m.s. discrepancy 11 values less than one 'loudspeaker unit' (i.e., less than 8.2°) whereas the majority of the sAPD group had 11 values greater than one unit. The difference in group means for 11 was statistically significant; however, the means were not very different and there was considerable overlap between the two groups. In the main study the control group performed better than the sAPD group [F(l, 62) = 28.9, p < 0.001], performance when listening in quiet was better than when listening in noise, and there was no interaction between subject group and listening condition. As previously observed in the pilot study, group means in the main study were all relatively similar and there was considerable overlap between the data sets. In relation to the hypotheses listed above, it may be concluded that the results from the pilot study and the main study confirm the first two hypotheses but not the third hypothesis. Although the data obtained in both studies indicate inferior localisation performance in the sAPD gro~ps compared to the control groups, all participants perform tolerably well and there is little evidence that the localisation performance of any member of the sAPD group would appear anomalous in everyday situations. At the end of this project, the suspicion remains that the association of localisation problems with APD has arisen largely by inference from the established link between localisation and central auditory processing. Hence it may be concluded that the accepted defmitiqns of APD (ASHA Working Group on APD, 2005; BSA APD Interest Group, 2003) should not be used at face value because their statements on localisation in APD are ambiguous or perhaps misleading.