The photochemistry of 2-naphthylsulfonyl azide (2-NpSO2N3) was studied by femtosecond time-resolved infrared (TR-IR) spectroscopy and with quantum chemical calculations. Photolysis of 2-NpSO2N3 with 330 nm light promotes 2-NpSO2N3 to its S1 state. The S1 excited state has a prominent azide vibrational band. This is the first direct observation of the S1 state of a sulfonyl azide, and this vibrational feature allows a mechanistic study of its decay processes. The S1 state decays to produce the singlet nitrene. Evidence for the formation of the pseudo-Curtius rearrangement product (2-NpNSO2) was inconclusive. The singlet sulfonylnitrene 1(2-NpSO2N) is a short-lived species (τ ≈ 700 ± 300 ps in CCl4) that decays to the lower-energy and longer-lived triplet nitrene 3(2-NpSO2N). Internal conversion of the S1 excited state to the ground state S0 is an efficient deactivation process. Intersystem crossing of the S1 excited state to the azide triplet state contributes only modestly to deactivation of the S1 state of 2-NpSO2N3.