About half of people infected with Human Immunodeficiency Virus (HIV) often present late for care, resulting in higher healthcare costs, undesired treatment outcomes, and ongoing HIV transmission. This study aimed to assess the prevalence and determinants of late HIV diagnosis and advanced HIV disease (AHD) in Tanzania. Data were obtained from the 2016-17 Tanzania HIV impact survey. We included 677 newly diagnosed people living with HIV. Late HIV diagnosis and AHD were defined as having a CD4 cell count below 350 cells/µL or 200 cells/µL at diagnosis, respectively. Bivariate and multivariable logistic regression models were fitted to identify the determinants of late HIV diagnosis or AHD. The mean age of the participants was 37.8 years (SD, 12.4). About two-thirds were women (62.6%). The prevalence of late HIV diagnosis was 42.4%, whereas the prevalence of AHD was 17.7%. Factors associated with late HIV diagnosis included age 31-40 years (adjusted odds ratio [aOR] = 1.72, 95% confidence interval [CI]: 1.14-2.60), age ≥41 years (aOR = 1.79, 95% CI: 1.16-2.76), male sex (aOR = 1.88, 95% CI: 1.29-2.73), and active syphilis infection (aOR=2.63, 95% CI: 1.20-5.76). Factors associated with AHD were age 31-40 years (aOR = 2.12, 95% CI: 1.18-3.81), age ≥41 years (aOR = 2.42, 95% CI: 1.32-4.41), male sex (aOR = 1.77, 95% CI: 1.09-2.87), formal education (aOR = 0.49, 95% CI: 0.30-0.81) and active syphilis infection (aOR = 2.49, 95% CI: 1.07-5.77). Late HIV diagnosis and AHD are prevalent among newly diagnosed people living with HIV in Tanzania. Specific subgroups are more likely to present late for HIV care, including middle-aged and older adults, men, illiterate individuals, and those with active syphilis and HIV co-infection. Therefore, we recommend expanding HIV testing services and implementing targeted interventions to improve early access and enrollment in HIV care.