Context: The absence of classical symptoms and signs of hyperthyroidism often results in delayed diagnosis and treatment. Objectives: The objective of the study was to determine the prevalence of symptoms and signs of hyperthyroidism according to patients' age and gender as well as severity and type of hyperthyroidism. Design, Participants and Setting: This was a cross-sectional study of 3049 consecutive patients with hyperthyroidism presenting to a single secondary/tertiary care clinic. Main Outcome Measures: Calculation of adjusted odds ratios for presence/absence of symptoms/signs of hyperthyroidism simultaneously analyzing the influence of patients' age/gender, disease etiology/severity, symptom duration, and smoking. Results: The majority of patients older than 61 yr had two or more symptoms. The lowest proportion of subjects reporting five or more symptoms was found in those older than 61 yr. Increasing age was associated with reduced adjusted odds ratio for the presence of most classical symptoms except for weight loss and shortness of breath, independent of disease severity. Those with more severe hyperthyroidism and smokers had increased odds ratios for most symptoms. Older age, higher serum free T4 concentrations at diagnosis, male gender, and toxic nodular hyperthyroidism were independently associated with risk of atrial fibrillation. Signs of ophthalmopathy were associated with increasing age, smoking, longer symptom duration, and female gender. Conclusions: Classical symptoms and signs of hyperthyroidism are significantly less prevalent in older patients and more prevalent in smokers and subjects with higher free T4 concentrations. We propose a lower threshold for performing thyroid function tests in patients older than 60 yr, especially in those presenting with atrial fibrillation, weight loss, or shortness of breath.