We examined the results of the Northwest Regional Screening Program (NWRSP) over its first 10 years to determine whether the detection of hypopituitary hypothyroidism is a justified advantage of the primary thyroxine (T4)-supplemental thyroid-stimulating hormone (TSH) screening strategy, and to determine whether all such infants will be detected by this screening approach. Between May 1975 and May 1985, the NWRSP screened 850,431 infants, detecting 192 infants with primary hypothyroidism (1:4429) and eight with hypopituitary hypothyroidism (1:106,304). In 11 additional infants, TSH deficiency, not detected by the screening program, was diagnosed on recognition of clinical features over the same period. Thyroid hormone treatment was begun in seven of the 11 infants prior to obtaining the screening sample results because of clinical symptoms of hypopituitarism, including hypoglycemia, persistent jaundice, microgenitalia, diabetes insipidus, midface hypoplasia, cleft lip or palate, or abnormalities of vision. The other four infants were not detected despite clinical features of hypopituitarism (in retrospect) and low serum T4 with TSH concentration below assay sensitivity on at least one screening sample. The most accurate assessment of total cases comes from Oregon, where all cases of congenital hypopituitarism are referred to our center; we estimate a frequency of 1:29,000. In our experience, a combination of newborn T4-supplemental TSH screening measurements and recognition of clinical features of hypopituitarism is the optimal strategy for detecting infants with congenital hypopituitary hypothyroidism.