Ultra narrow row (UNR) cotton production has been proposed as an economical means to increase cotton pro- duction efficiency . Advantages of a UNR production system include earlier crop development, reduced costs from late season insect control, and in some cases, increased yields .A field study was conducted to investigate the effects of population density and arsenic rate on yield, growth, and fiber response of ultra narrow row (UNR) cotton. Stand loss occurred at densities greater than 22 plants m−2 and arsenic rates greater than 56 kg ha−1 and stand loss exceeded 20% at harvest. Seed cotton yields were similar across populations and rates of 56, 112, and 168 kg ha−1 . Arsenic rates greater than 56 kg ha−1 resulted in greater vegetative growth based on increased plant height and number of nodes. These results indicate that populations of 22 plants m−2 and arsenic rates of 56 kg ha−1 were sufficient for maximum yields in UNR cotton under our conditions. However, at higher arsenic rates, boll formation increased at lower nodes with no corresponding change in yield. Higher arsenic rates may promote earliness and distribute yield across more fruiting sites.