The Patterns of Care Study (PCS) conducted two national surveys of patients treated in 1973 and 1978 for squamous cell cancer of the uterine cervix. In addition, a survey of patients treated in 1973 from selected large facilities was conducted to establish outcome with "optimal" radiotherapy. The large facility survey consistently reported improved outcome compared to both national average surveys when analyzed by stage and other significant pretreatment factors. That improved outcome was associated with the paracentral (PCS point A) dose and the use of intracavitary irradiation. In this study, we report the pretreatment and treatment factors associated with improved outcome in squamous cell carcinoma of the uterine cervix by analysis of the 1973 and 1978 PCS data. Pretreatment factors associated with improved pelvic control in multivariate analysis include higher Karnofsky Performance Status (KPS) (Stage I and II), older age (Stage I and II), unilateral parametrial involvement (Stage IIB), and unilateral sidewall involvement (Stage III). The only treatment factor associated with improved pelvic control in multivariate analysis is the use of intracavitary irradiation. However, a dose response for infield pelvic control was demonstrated only in Stage III cervix cancer with the highest rate of pelvic control with paracentral (PCS point A) dose greater than 8500 cGy. Multivariate analysis revealed that unilateral parametrial involvement for Stage IIB and unilateral sidewall involvement for Stage III are significant positive prognostic factors with respect to survival after treatment with radiotherapy. No FIGO substage significantly affected survival after radiotherapy. Although FIGO staging is the single most important pretreatment prognostic factor with respect to survival and infield pelvic failure, FIGO substaging deserves reappraisal and further refinement. Major complications were seen in only 9.5% of patients treated with radiotherapy and were stage but not survey related. There is a significant relationship between PCS point A dose and complications with the highest rate of complications for PCS point A dose greater than 8500 cGy. A significant relationship between lateral (external iliac lymph nodes or PCS point P) dose and major complications is also found, and doses greater than 5000 cGy are associated with a significant increase in complications. The PCS has established two sequential national benchmarks of treatment outcome for squamous cell carcinoma of the uterine cervix treated with radiotherapy with respect to survival, infield pelvic control, and complications.(ABSTRACT TRUNCATED AT 400 WORDS)