Cells infected with a number of alphaherpesviruses produce non-infectious virion-related particles, termed L particles, in addition to infectious virions. L particles consist of the tegument and envelope components, but lack the virus capsid and DNA. Using a herpes simplex virus type 1 (HSV-1) temperature-sensitive mutant, ts1201, which fails to produce mature virions, we show that L particle production is independent of virion formation. Moreover, the quantity and protein composition of L particles generated by this mutant at the non-permissive temperature are indistinguishable from those produced in wild-type HSV-1 infections. Electron microscopy studies suggest that the processes governing the assembly of tegument and envelope components into L particles are similar to those involved in virion maturation.