OBJECTIVE To determine the prevalence of white spot lesions (WSLs) in orthodontic patients at 6 and 12 months into treatment using the visual examination method. METHODS Patients 6 and 12 months into treatment were examined for the presence of WSLs. The control group consisted of patients who were examined for WSLs immediately after bonding. Upon clinical evaluation, teeth were given a visual score based on the extent of demineralization. RESULTS The percentages of individuals having at least one WSL were 38%, 46%, and 11% for the 6-month, 12-month, and control groups, respectively. The 6-month (P  =  .021) and 12-month groups (P  =  .005) were significantly different from the control group but were not significantly different from each other (P  =  .50). Of subjects in the study who had at least one visible WSL, 76% were males and 24% were females (P  =  .009). CONCLUSIONS This clinical study showed a sharp increase in the number of WSLs during the first 6 months of treatment that continued to rise at a slower rate to 12 months. Clinicians should evaluate the oral hygiene status of patients during the initial months of treatment and, if necessary, should implement extra measures to prevent demineralization.