HIV serostatus disclosure plays an important role in HIV transmission risk reduction and is positively associated with HIV medication adherence and treatment outcomes. However, to date, no study has quantified the role of disclosure across the HIV treatment cascade, particularly in Sub-Saharan Africa. We used data from a cohort of HIV-infected adults in Northern Tanzania to describe associations between disclosure and engagement and retention in the HIV treatment cascade. Between 2008 and 2009, the Coping with HIV/AIDS in Tanzania (CHAT) study enrolled 260 clients newly diagnosed with HIV and 492 HIV-infected patients in established HIV care in two large HIV care and treatment centers in Northern Tanzania. Participants aged 18 and older completed annual clinical assessments and twice-annual in-person interviews for 3.5 years. Using logistic regression models, we assessed sociodemographic correlates of HIV serostatus disclosure to at least one household member, and associations between this disclosure measure and linkage to care, evaluation for antiretroviral therapy (ART) eligibility, ART coverage, and rates of undetectable HIV RNA levels during the follow-up period. Married individuals and those diagnosed earlier were more likely to have disclosed their HIV infection to at least one household member. During follow-up, HIV serostatus disclosure was associated with higher rates of linkage to care, evaluation for ART eligibility, and ART coverage. No significant association was observed with rates of undetectable viral loads. Marginal effects estimates suggest that a 10 percentage-point lower probability of linkage to care for those who did not disclose their HIV serostatus (86% vs. 96%; p = 0.035) was compounded by an 18 percentage-point lower probability of ever receiving a CD4 count (62% vs. 80%; p = .039), and a 20 percentage-point lower probability of ever receiving ART (55% vs. 75%; p = .029). If causal, these findings suggest an important role for disclosure assistance efforts across the HIV treatment cascade.