We describe a 42-year-old woman who presented at our outpatient clinic complaining of redness, photophobia, and a white spot lesion in her right eye during the previous month. She had had carcinoma of the breast 4 years earlier for which she had undergone surgery, radiotherapy, and chemotherapy. At presentation, her visual acuity was 20/25 in the right eye and 20/20 in the left eye. A slit-lamp examination of the right eye showed ciliary injection and multiple fleshy yellow iris nodules with angle involvement. Suspecting a metastatic iris tumor, we conducted a thorough search for the primary tumor. Bilateral diagnostic mammograms showed evidence of breast-conserving surgery on the left side but no mammographic sign of malignancy. A whole-body bone scan revealed no active radioactivity uptake, and levels of α-fetoprotein, carcinoembryonic antigen, cancer antigen (CA)125, and CA153 were within normal ranges. A chest X-ray showed a mass over the right upper lobe and a computed tomography (CT) scan revealed a lobulated soft-tissue mass of 4 cm diameter. In these circumstances, malignancy should be considered first. Magnetic resonance imaging of the brain, with contrast, showed multiple enhanced nodular lesions over the cerebrum and cerebellum. A CT-guided needle biopsy of the lung mass was performed and poorly differentiated primary non-small-cell lung cancer was reported. Successful control of the lung malignancy was achieved after chemotherapy and radiotherapy, and concomitant regression of the iris nodules was noted in the 5-month follow-up.