Describes construction and tests validity of the Primary Care Anxiety and Depression (PCAD) Scale, an Arabic screening scale for anxiety and depression among primary health care (PHC) patients. The scale can be self-administered, but due to high illiteracy levels, will most likely be administered by nurses or other health personnel. Scale items were selected from a pool of items chosen from 2 international screening scales that were validated locally, the Self-Reporting Questionnaire and the Hospital Anxiety and Depression Scale (Arab versions). Results of validation with a new sample of PHC patients (aged 16-65 yrs) indicates that the PCAD Scale is a valid instrument for detecting clinically significant anxiety and depression in patients attending PHC clinics. The scale also shows a closer correlation with the independent psychiatrist's clinical judgement than with the general practitioner's assessment. Results indicate that all PCAD items are valid and each is highly correlated with the total of other items. Two cut-off points were established, one more appropriate for clinical use, and the other for prevalence estimation. The former threshold of the scale could be used to alert busy general practitioners to clinically significant anxiety or depression.