Strongyloides stercoralis
infections, human T-lymphotropic virus (HTLV) infections, and Chagas diseases occur throughout many regions of Central and South America, including Peru. This study aimed to evaluate the seroprevalence of
S. stercoralis
, HTLV, and Chagas disease in Iquitos (Peruvian Amazon) and the associated epidemiological conditions for
S. stercoralis
seroprevalence in Iquitos. A population-based cross-sectional study was conducted from May 1 to June 15, 2020, to assess the seroprevalence of
S. stercoralis
[lysate antigen ELISA (enzyme linked immunosorbent assay)], HTLV (recombinant antigen ELISA), and Chagas disease (crude and recombinant antigen ELISAs). Of the 396 included individuals, 257 were seropositive for
S. stercoralis
(a 64.9% prevalence, 95% confidence interval [CI] 60.0% to 69.4%). In the multivariable analysis, seropositivity for
S. stercoralis
was higher in women (odds ratio [OR] 1.60, 95% CI 1.03 to 2.66) and residents of Punchana (OR 3.47, 95% CI 1.51 to 7.93), whereas residence in Iquitos was associated with lower positivity (OR 0.52, 95% CI 0.32 to 0.85). In total, four individuals were positive for HTLV (1.0% seroprevalence, 95% CI 0.3% to 2.7%), and none were positive for Chagas disease (0.0% seroprevalence, 95% CI 0.0% to 1.2%). The seroprevalence of
S. stercoralis
in Iquitos is high, particularly among women and residents of Punchana. The presence of HTLV infection indicates that the virus is circulating in Iquitos. This study found no cases of Chagas disease.