Objective. To gain insight into general practitioners' (GPs) test-ordering behavior for patients presenting with unexplained complaints. An unexplained complaint's symptoms are not alarming, and there is no plausible medical or psychosocial explanation for it. The Dutch College of General Practitioners (DCGP) recommends a watchful, waiting attitude for test ordering for unexplained complaints. Methods. Observational, cross-sectional study of 567 doctor-patient consultations performed by 21 GPs. Results. On average, 13% of consultations involved complaints considered unexplained by GPs. Unexplained complaints were positively related to test ordering (adjusted odds ratio [OR] = 2.4, 95% confidence interval [CI] 1.1-5.3), despite the DCGPs recommendation. Patients' expectations about testing influenced test ordering even more (adjusted OR = 4.1, 95 % CI 2.2-7.6). Discussion. Unexplained complaints happen daily in general practice. Besides the DCGPs recommendation, factors such as GPs' desire to understand complaints and patients' expectations seem to have impacts. Guideline development and quality improvement projects should respect, next to Bayesian rules, GP- and patient-related determinants of test ordering. Key words: nonspecific complaints; unexplained complaints; general practice; physicians' practice patterns; test-ordering behavior; physician-patient relations; patient preferences. (Med Decis Making 2003;23:226-231).