Murine gammaherpesvirus (MHV)‐68‐infected mice are well‐known as models for Epstein–Barr virus (EBV)‐related lymphoproliferative diseases. MHV‐72 may be a relative of MHV‐68, but any genetic comparison between the two (except for the M7 gene) has never been reported. The genetic compositions of MHV‐72 and MHV‐68 were compared and the pathology of MHV‐72 infection studied in CB‐17 severe combined immunodeficiency (scid/scid; SCID) and CB17 wild‐type (CB17+/+) mice. The MHV‐72 DNA sequence was almost identical to MHV‐68 except for approximately 7000 bp corresponding to the MHV‐68 M1–M3 genes. Twenty‐seven of 30 MHV‐72‐infected SCID mice (90%) died from generalized infection with intranuclear viral inclusions for approximately 1 month, while MHV‐72‐infected CB17+/+ mice recovered from acute infection. Long observation and pathological study of 68 MHV‐72‐infected mice for up to 24 months revealed that the survival rate (29.4%) and survival time (21.3 months) of MHV‐72‐infected CB17+/+ mice were significantly lower (P = 0.0127) and shorter (P = 0.0065) than those of the controls (61.1% and 22.9 months), respectively. The malignancy development rate (60.3%) of the infected CB17+/+ mice was also significantly higher (P = 0.004) than those of the controls (22.2%). However, no MHV‐72 DNA was detected in the tumors of infected mice. MHV‐72 may have some tumor‐promoting effects but the tumorigenesis in infected CB17+/+ mice is different from EBV‐associated tumors.