Purpose: The incidence of severe combined immunodeficiency (SCID) in the USA was reported as 1 in 58,000 live births. In Arizona, it was anticipated that newborn screening would identify two to four cases of SCID per year. This estimate did not consider ethnic nuances in Arizona, with higher percentages of Native American and Hispanic populations compared to national percentages. The true incidence of SCID and non-SCID T cell lymphopenia has not previously been reported in Arizona., Methods: A retrospective chart review was performed on all abnormal SCID newborn screening (NBS) tests in Arizona from January 1, 2018, to December 31, 2019, using data from the Arizona Department of Health Services and the Phoenix Children's Hospital's electronic medical record [IRB# 20-025]., Results: Seven infants were diagnosed with SCID, yielding an incidence of 1 in 22,819 live births. Four of these infants had Artemis-type SCID. Thirteen infants were identified with an abnormal initial NBS which ultimately did not lead to a diagnosis of SCID. Four of these infants were diagnosed with congenital syndromes associated with T cell lymphopenia. Infants of Hispanic ethnicity were over-represented in this cohort., Conclusion: Over 2 years, NBS in Arizona confirmed an incidence more than 2.5 times that reported nationally. This increased incidence is likely reflective of Arizona's unique population profile, with a higher percentage of Native American population. The findings in our non-SCID cohort are in alignment with previously published data, except for an increased percentage of infants of Hispanic/Latino ethnicity, possibly reflecting Arizona's increased percentage of Hispanic/Latino population compared to the general US population., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)