Ultrasound (US) has been demonstrated to be the method of choice for diagnosing luteinized unruptured follicle syndrome and to be a valuable adjuvant in the assessment of luteal phase defect. In this prospective study, the use of US with postcoital testing (PCT) is evaluated. Fifty control infertility patients were examined with serial US for follicle dynamics in conjunction with PCT. Standard curves for follicle dynamics versus cervical mucus quality (Insler score) were calculated. Eighteen patients referred for abnormal mucus underwent similar evaluation. Their follicle dynamics versus mucus quality were compared with those of the controls. The findings were: (1) there is a predictable relationship between follicle size and mucus quality, (2) the majority of patients with abnormal mucus have normal follicular dynamics, and (3) a minority of patients with abnormal mucus have either a narrow mucus window or abnormal follicular dynamics. In addition, US was found to be cost-effective in the overall fertility evaluation.